KR102689128B1 - Photosensor using flexoelectricity effect and bio diagnostic apparatus - Google Patents

Abstract

An optical sensor that detects the presence or movement of a target is disclosed. The optical sensor includes a light source that irradiates light in the direction of a target object; A sensing element that generates a photocurrent by receiving light reflected by the target or light transmitted through the target; and a current meter that measures photocurrent. The sensing element includes a dielectric thin film formed of a dielectric material that has a centrally symmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region; An electrode disposed on one side of the dielectric thin film, made of a transparent conductive material that transmits light in the infrared or visible light region, and electrically connected to a current meter; and a local force applicator that applies local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film.

Description

Optical sensor using transformation effect and bio diagnostic device equipped with the same {PHOTOSENSOR USING FLEXOELECTRICITY EFFECT AND BIO DIAGNOSTIC APPARATUS}

The present invention relates to an optical sensor capable of detecting light using a dielectric such as a semiconductor and a bio-diagnostic device equipped with the same.

The breaking of spatial inversion symmetry across a centrosymmetric dielectric induces a spontaneous electric polarization field along the preferred direction due to the strain gradient, known as the transformation effect. When using this transformation effect, it is expected that photocurrent can be generated under zero bias conditions.

However, for optical sensors using transformation effects, only basic matters such as adjustment of the band gap are still reported, so more in-depth research is needed.

One object of the present invention is to provide an optical sensor capable of detecting light with significantly improved performance by causing local strain in a dielectric thin film and adjusting its bandgap.

Another object of the present invention is to provide a bio-diagnosis device including the optical sensor.

An optical sensor according to an embodiment of the present invention can detect the presence or movement of a target, and includes a light source that irradiates light in the direction of the target; a sensing element that generates a photocurrent by receiving light reflected by the target or light transmitted through the target; and a current meter that measures the photocurrent, wherein the sensing element includes: a dielectric thin film formed of a dielectric material having a centrosymmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region; an electrode disposed on one surface of the dielectric thin film, formed of a transparent conductive material that transmits light in the infrared or visible light region, and electrically connected to the current meter; and a local force applicator that applies local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film.

In one embodiment, the light source irradiates light containing an infrared wavelength, and the dielectric thin film in which the strain is caused may absorb light having energy less than the fundamental bandgap to generate the photocurrent.

In one embodiment, the dielectric thin film may be formed of a semiconductor material having a fundamental bandgap of 1 to 3 eV.

In one embodiment, the localized force applicator may include a point tip having a spherical or hemispherical shape.

In one embodiment, the electrode includes a conductive metal nanowire electrode, a conductive metal electrode with a mesh structure, a conductive carbon material electrode, a transparent conductive oxide electrode, or a transparent conductive polymer electrode, and a short circuit is formed at the interface between the electrode and the dielectric thin film. A key barrier can be formed.

In one embodiment, the electrode includes an opening that exposes a portion of the surface of the dielectric thin film, and the local force applicator may apply a local force to the surface of the dielectric thin film through the opening.

An optical sensor according to an embodiment of the present invention includes a dielectric thin film formed of a dielectric material that has a centrosymmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region; an electrode disposed on one surface of the dielectric thin film and formed of a transparent conductive material capable of transmitting light in the infrared region; and a local force applicator that applies a local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film. a light source that irradiates light in the direction of the sensing element; and a current meter electrically connected to the electrode and measuring a photocurrent formed in the dielectric thin film by the light.

In one embodiment, the dielectric thin film may be formed of a semiconductor material having a fundamental bandgap of 1 to 3 eV.

In one embodiment, the light source irradiates light containing an infrared wavelength, and the strain-induced dielectric thin film may absorb light of the infrared wavelength having an energy less than the fundamental bandgap to generate the photocurrent. there is.

A bio-diagnosis device according to an embodiment of the present invention is capable of diagnosing the health status of a human body or an animal, and includes a light source that irradiates light toward the human body or animal; an array of a plurality of sensing elements each receiving light reflected by the human body or animal or light transmitted through the human body or animal and generating a photocurrent; and a current meter that measures photocurrents generated by the sensing elements, each of the sensing elements having a centrally symmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region. A dielectric thin film formed of a dielectric material having; an electrode disposed on one surface of the dielectric thin film, formed of a transparent conductive material that transmits light in the infrared or visible light region, and electrically connected to the current meter; and a local force applicator that applies local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film.

According to the optical sensor and bio-diagnosis device of the present invention, the band gap of the dielectric thin film and the dielectric thin film and the electrode are determined through a transformation effect polarization field generated by inducing a local strain in the dielectric thin film through the local force applicator. The Schottky barrier can be adjusted, and as a result, the target can be detected in real time and with high sensitivity without the use of external power.

1A and 1B are diagrams for explaining optical sensors according to an embodiment of the present invention.
Figure 2 is a diagram for explaining an optical sensor according to another embodiment of the present invention.
Figure 3 shows the qualitative strain distribution in silicon along the xz plane ('a'), calculated by Hertzian contact theory using a point tip with a hemispherical tip, and the bandgap adjustment ('b') depending on the applied force, for various applied forces. It shows the IV curve measured against force ('c') and the change graph of forward and reverse current according to applied force ('d').
Figure 4 shows IV curves ('a'), Graph showing the variation of photocurrent with light intensity ('b'), graph showing the change in photocurrent with wavelength measured for various applied forces under self-bias (0 V) and fixed light intensity (0.2 mW cm ^-2 ) conditions. Change graph ('c', 'd') and change of photocurrent over time when pulsed light (λ=1620nm) with different irradiation intensities is irradiated under conditions of application of fixed force using self-bias and Au-coated probe. Represents a graph ('e').
Figure 5 shows a current map ('a') collected by changing the tip voltage (V _tip ) from +0.1/-0.1 V to +0.4/-0.4 V with a period of 0.1 V under light irradiation conditions, Vtip= Current map of the device collected under zero and dark conditions ('b'), current map collected under self-bias and continuous white light irradiation conditions ('c'), fixed applied force and pulsed light irradiation (P=2 mWcm). ^-2 ) Self-biased instantaneous photoresponse graph ('d') of the device collected from a fixed position using a cAFM tip (diameter = 35 nm) under conditions ('e'), graph showing the force-dependent photocurrent characteristics ('e') and Shows a graph ('f') measuring the change in photocurrent size according to the applied force.
Figure 6 is a graph ('a') showing the change in sensitivity (S) of the device to an applied point force for a fixed light irradiation of P=2 mWcm ^-2 and the intensity of the irradiation light for a fixed force of 4 μN. A graph ('b') showing the change in response (R) and sensitivity (D) according to is shown.

Hereinafter, embodiments of the present invention will be described in detail. Since the present invention can be subject to various changes and can have various forms, specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention. While describing each drawing, similar reference numerals are used for similar components. In the attached drawings, the dimensions of the structures are enlarged from the actual size for clarity of the present invention.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as “comprise” or “have” are intended to designate the presence of features, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features or steps. , it should be understood that it does not exclude in advance the possibility of the existence or addition of operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

1A and 1B are diagrams for explaining optical sensors according to an embodiment of the present invention.

1A and 1B, the optical sensor (100a, 100b) according to an embodiment of the present invention may include a light source (110a, 100b), a sensing element (120a, 120b), and a current meter (130a, 130b). You can.

The light sources 110a and 110b may irradiate light containing an infrared wavelength to the target 10 to be sensed. For example, the light sources 110a and 110b may irradiate light containing an infrared wavelength of about 1100 to 1700 nm toward the target 10. The light sources 110a and 110b may emit continuous light or pulsed light.

The sensing elements 120a and 120b may generate photocurrent by receiving light reflected by the target 10 (see FIG. 1A) or light transmitted through the target 10 (FIG. 1B). In one embodiment, the sensing elements 120a and 120b may include dielectric thin films 121a and 121b, local force applicators 122a and 122b, and electrodes 123a and 123b.

The dielectric thin films 121a and 121b may be formed of a dielectric material that has central symmetry and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region. For example, the dielectric thin films 121a and 121b may be formed of a semiconductor material with a band gap of about 1 to 3 eV.

The local force applicators 122a and 122b may apply local force to the surfaces of the dielectric thin films 121a and 121b, causing non-uniform strain in the dielectric thin films 121a and 121b. As long as local force can be applied to the surface of the dielectric thin films 121a and 121b, the shape and structure of the local force applicators 122a and 122b are not particularly limited. For example, the local force applicators 122a and 122b may include point tips whose tips for pressing the dielectric thin films 121a and 121b have a spherical or hemispherical shape.

When a non-uniform strain having a gradient is caused in the dielectric thin films 121a and 121b by the local force applicators 122a and 122b, the transformation effect polarizes the dielectric thin films 121a and 121b due to the destruction of central symmetry. Fields can be derived. For example, the effect of the force applied by the local force applicator 122a, 122b does not remain locally in the dielectric thin film 121a, 121b, but it destroys spatial symmetry over a long region, thereby causing This causes electromagnetic rearrangement, which can change the band gap of the dielectric thin films 121a and 121b. That is, the local point force applied by the local force applicators (122a, 122b) can generate a long-area distributed transformation effect polarization field within the dielectric thin films (121a, 121b) and at the same time reduce the effective band gap. . When a transformation effect polarization field is generated in the dielectric thin films 121a and 121b and the effective band gap is reduced, the induced polarization field redistributes available free carriers not only at the metal-dielectric interface but also within the dielectric, thereby This can lead to changes in the band arrangement, and the reduced effective bandgap can change the effective Schottky barrier (both height and width) between the metal and dielectric, thereby controlling the overall charge transfer.

In one embodiment, when the dielectric thin films 121a and 121b are formed of single crystal silicon with a fundamental bandgap of about 1.12 eV, the local strain caused by the local force applicators 122a and 122b The band gap of the silicon thin film can be reduced to about 0.5 eV.

The electrodes 123a and 123b may be disposed on one surface of the dielectric thin films 121a and 121b, and may be made of a transparent conductive material through which light reflected from or transmitted through the target 10 can be transmitted. It can be formed as In one embodiment, the electrodes 123a and 123b may include a conductive metal nanowire electrode, a mesh-structured conductive metal electrode, a conductive carbon material electrode, a transparent conductive oxide electrode, a transparent conductive polymer electrode, etc.

Meanwhile, the local force applicators 122a and 122b may cause local strain in the dielectric thin films 121a and 121b by pressing the electrodes 123a and 123b, and may cause local strain in the electrodes 123a and 123b. After forming an opening that exposes a portion of the surface of the dielectric thin film (121a, 121b), local strain is applied to the dielectric thin film (121a, 121b) by directly pressing the surface of the dielectric thin film (121a, 121b) through the opening. may cause.

When light reflected from the target 10 or transmitted through the target 10 is incident on the dielectric thin films 121a and 121b in which strain is generated by the local force applicators 122a and 122b, the dielectric The thin films 121a and 121b can absorb photons of a wider wavelength band to generate electron-hole pairs due to a decrease in the band gap, and the thin films 121a and 121b can generate electron-hole pairs between the electrodes 123a and 123b and the dielectric thin films 121a and 121b. By adjusting the height and width of the effective Schottky barrier, the electrons and holes of the electron-hole pair can be rapidly separated to generate more sensitive photocurrent.

Meanwhile, the dielectric thin films 121a and 121b may be supported by the substrates 140a and 140b. The structure and material of the substrates 140a and 140b are not particularly limited as long as they can support the dielectric thin films 121a and 121b.

The current meters 130a and 130b are electrically connected to the electrodes 123a and 123b to measure the photocurrent generated by the dielectric thin films 121a and 121b, thereby determining the presence or internal state of the object 10. It can be detected. As long as the photocurrent generated from the dielectric thin films 121a and 121b can be measured, the structure of the current meters 130a and 130b is not particularly limited.

Figure 2 is a diagram for explaining an optical sensor according to another embodiment of the present invention.

Referring to FIG. 2, an optical sensor 200 according to another embodiment of the present invention may include a light source 210, a sensing element 220, and a current meter 230.

In the case of the optical sensor 200 of this embodiment, FIGS. 1A and 1B except that the light source 210 irradiates light in the direction of the electrode 223 or the dielectric thin film 222 of the sensing element 220. Since it is substantially the same as the optical sensors 100a and 100b described with reference to , redundant detailed description will be omitted below.

Meanwhile, the optical sensors 100a, 100b, and 200 according to the present invention do not have a separate light source and can detect an object or infrared rays using light generated from sunlight or household lighting.

According to the optical sensors of the present invention, the band gap of the dielectric thin film and the short circuit between the dielectric thin film and the electrode are generated through a transformation effect polarization field generated by inducing a local strain in the dielectric thin film through the local force applicator. The key barrier can be adjusted, and as a result, the target can be detected in real time and with high sensitivity without the use of external power.

The optical sensors of the present invention can be applied to a sensing device that detects the presence or movement of an object or person, or a bio-diagnostic device that diagnoses the state of the human body by arranging a plurality of sensing element cells.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the following examples are only some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

Commercially available n-type silicon (resistance = 1-10 Ωcm) was used to study the effect of applied force. The silicone was supported on a solid surface to prevent it from breaking. Before measurement, the silicon wafer was ultrasonically cleaned with acetone, isopropyl alcohol, and distilled water sequentially for 15 minutes each and then dried with nitrogen gas. To remove native oxide, the silicon was etched by buffered HF solution for 5 min. Bulk force was applied by an Au-coated probe (diameter = 120 μm).

[Experimental example]

Figure 3 shows the qualitative strain distribution in silicon along the xz plane ('a'), calculated by Hertzian contact theory using a point tip with a hemispherical tip, and the bandgap adjustment ('b') depending on the applied force, for various applied forces. It shows the I-V curve measured against force ('c') and the change graph of forward and reverse current according to applied force ('d').

As shown in Figure 3 a, it can be seen that the local force applied using a point tip (diameter = 120 ㎛) with a hemispherical tip induces a non-uniform strain distributed over a long area ( = 960 ㎛). . As previously reported, spatial variation of strain, i.e., gradient, can induce a transforming effect polarization field, as shown by the white arrow in Figure 1 a. The effect of the applied point force does not remain locally, but it destroys spatial symmetry over long regions, which can cause electromagnetic rearrangements. This induced electromagnetic rearrangement is expected to change the effective bandgap of silicon.

As shown in Figure 3b to illustrate the concept of transformation effect-induced wide band light absorption, the effective band gap of silicon can be reduced to about 0.5 eV due to the applied strain. Local point forces can mainly cause two effects: the generation of a long-area distributed transforming polarization field and the resulting reduction in the effective bandgap, which can act together to dominate the overall optoelectronic performance. You can. For example, the induced polarization field redistributes available free carriers at the metal-semiconductor interface as well as inside the semiconductor, which can cause band arrangement changes at the interface. Additionally, the strain-tunable bandgap can vary the height and width of the effective Schottky barrier, which can tune the overall charge transfer. In fact, the role of applied strain in changing the bandgap of silicon can be confirmed by density functional theory, and the effective bandgap of silicon decreased as the applied strain increased.

Referring to Figure 3 c, which shows the current-voltage (I-V) characteristics of single crystal n-type silicon corresponding to different forces applied using an Au-coated tip (diameter = 120 μm), charge transfer is dependent on the external force ( That is, it is clearly confirmed that it can be greatly adjusted by applying strain. Specifically, the I-V curve shows asymmetric behavior where the forward current increases and becomes larger than the reverse current at a critical force of approximately 4 μN. The device showed typical rectifying behavior when a force of 5 μN or more was applied.

As shown in Figure 3d, for the maximum current at +1.0 V (forward) and -1.0 V (reverse), the forward current gradually increases as the applied force increases, while the reverse current increases with the applied force. It was found to remain unchanged in response to force, confirming that the electromagnetic rearrangement mechanism is possible by the applied force.

The mechanisms governing the observed I-V curve as the applied force increases are complex. Various factors such as changes in contact area, effective bandgap, generation of transformation potential, generation of local force induction of surface potential, etc. can contribute to changes in the I-V curve. Therefore, we believe that in-depth research is needed to understand the connection between these effects and the extraction of dominant roles. Changes in the I-V curve are not just caused by changes in contact area; several other factors, such as transformation effects, can contribute to charge transfer.

It has been reported that transformation effect polarization can effectively control carrier distribution inside and at the interface barrier of silicon and thereby electromagnetic transmission in silicon. In fact, as the applied force increases, the induced polarization effect attracts holes while repelling electrons, thereby adjusting the barrier height. Depending on the applied force, not only does the effective band gap of silicon decrease, but the Schottky barrier height increases due to the strong polarization effect. These two effects work together to regulate overall charge transfer under forward bias conditions, while having no significant effect under reverse bias conditions. In fact, under reverse bias conditions, charge transfer is mainly dominated by local barriers, and thus the role of polarization is not dominant. The adjustment of I-V behavior according to the applied force is due to the generation of a strain gradient-induced transformation effect potential, which changes in size depending on the applied force, and as a result, the Schottky barrier can be adjusted.

Figure 4 shows IV curves ('a'), Graph showing the variation of photocurrent with light intensity ('b'), graph showing the change in photocurrent with wavelength measured for various applied forces under self-bias (0 V) and fixed light intensity (0.2 mW cm ^-2 ) conditions. Change graph ('c', 'd') and change of photocurrent over time when pulsed light (λ=1620nm) with different irradiation intensities is irradiated under conditions of application of fixed force using self-bias and Au-coated probe. Represents a graph ('e').

As shown in Figure 4 a, b, under self-bias (0 V) conditions, the short circuit current (Ish) is about 8.5 μA (i.e., upward shift of the current from 0 V) and about 0.37 V (i.e., the IV curve The open circuit voltage (shift of the voltage minimum from the origin) was recorded under light irradiation (P=2 mWcm ^-2 ) conditions, indicating the presence of the photoelectric effect. Therefore, it can be confirmed that the Au-tip/Si geometry responds well to light irradiation and can generate electron-hole pairs by light absorption. The photocurrent switching ratio (I _sh /I _dark ) (I _dark is a dark current of about 5.8×10 ^-11 A) reached about 10 ⁵ under light irradiation conditions of 2 mWcm ^-2 intensity. The photocurrent (I _ph =I _light -I _dark ) at 0 V gradually increased with light intensity, indicating that the density of electron-hole pairs generated by light is linearly related to photon absorption.

Additionally, the linear dynamic region (LDR) expressed by Equation 1 below was evaluated using Iph change according to light intensity.

[Formula 1]

As a result of the evaluation, the LDR was 103 dB, indicating excellent sensitivity to light irradiation. Additionally, these changes (where α is the exponent associated with governing the carrier recombination process). Basically, α values close to 1 indicate band-band recombination, and values close to 2 indicate defect-related Shockley-Read-Hall (SRH) recombination processes. In this example, an α value close to 1 (about 0.97) was extracted, confirming that the SRH process is not dominant in this example.

In addition, as the applied force changes from 1 μN to 8 μN, it is shown in Figure 4 c, d showing the change of Iph according to different wavelengths (λ = 300 ~ 1700 nm) with 0 V and fixed irradiation intensity. As can be seen, I _ph appeared for a wide band of light irradiation from ultraviolet (λ = 300 nm) to short-wave infrared (λ = 1700 nm), which is well beyond the fundamental band gap of silicon (Eg = 1.12 eV).

The magnitude of the photocurrent (I _ph ) was significantly dependent on the applied force. Specifically, at λ = 1620 nm, Iph increased from 0.45 nA to 120 nA as the applied force increased from 1 μN to 8 μN. This anomalous Iph beyond the bandgap of silicon and its tuning by the applied force was first observed, but it is not explained by an increase in the contact area of the crystalline and centrosymmetric Si or the applied force. But certainly, at 0 V bias, the notable Ip for λ≥100 nm is due to the generation of light absorption-induced electron-hole pairs and their rapid separation by junction, and the Ip and Ip depending on the applied force for λ=1100 nm. This adjustment is due to changes in the effective bandgap.

To find experimental evidence of point force-induced bandgap tuning, we independently measured the temperature-dependent change in resistance with point force and the geometry of bulk Au electrodes, and found that the effective bandgap of Si with point force applied was 0.4 eV. It was measured to be close to , which indicates that the change in band gap according to the applied force is significant. In this respect, the notable infrared photoresponse is believed to be due to the applied strain. On the other hand, the applied force not only reduces the effective bandgap at local positions, but also increases the effective area for absorbing photons with λ≥1100 nm, and as a result, Iph increases significantly in light irradiation of broadband wavelengths depending on the applied force. can be improved.

As shown in Figure 4 e, to confirm reproducible behavior, the instantaneous photoresponse was measured under pulsed light (λ=1620 nm) irradiation conditions with various intensities (P=0~2 mWcm ^-2 ) at 0V bias. (It) was measured. As expected from the wavelength-dependent spectrum, excellent photoresponse was observed at λ = 1620 nm without any external potential, confirming the generation of electron-hole pairs. However, unlike the conventional direct current photocurrent (I _dc ), an additional peak appeared during light-on conditions, indicating that an alternating current photocurrent (I _ac ) was also generated. The observed direct current photocurrent (I _dc ) is due to the classical photoelectric effect, but the additional peaks for centrosymmetric materials such as Si are due to a new type of effect called the alternating current photoelectric effect, which is due to periodic light at the junction/interface of the material. It appears through research. In fact, the rapid splitting and rearrangement of the quasi-Fermi level due to rapid changes in light irradiation conditions is the main source of these peaks, in other words, reverse electrons in the external circuit to maintain the potential difference between the two electrodes. and the peaks are generated by vibrating in the forward direction. Meanwhile, the size of Iac and Idc changed depending on the light intensity, but the size of the _Iac peak (=2.8 μA) was significantly higher than that of I _dc (=2.1 μA) under similar light irradiation conditions.

By operating the device at high speed, the photocurrent rise time (τ _r , the time required for the photocurrent to increase from 10% of the peak to 90%) and the fall time (τ _f , the time required for the photocurrent to decrease from 90% to 10% of the peak) As a result of measuring the time (time), it was 100 μs and 316 μs, respectively. Additionally, the cutoff frequency (f _3dB ) of the device at 3dB, evaluated using Equation 2 below, was 3.5 kHz.

[Formula 2]

This significantly higher response time allows the device to operate at high data rates. Additionally, the reproducibility of photocurrent generation and its point-to-point changes was checked by data collection from randomly selected positions (by shifting the measuring tip), and the standard deviation (σ) calculated from Equation 3 below: ) was 2.2%. This narrow and centralized distribution clearly confirms that the structure of the present invention exhibits high reproducible performance.

[Formula 3]

In equation 3, n represents the number of measurements and I _ph (mean) represents the average photocurrent over all measurements.

In addition, the results of measuring IV curves under dark and light irradiation conditions of λ = 1620 nm showed the appearance of a built-in potential of about 0.15 V and a photocurrent of about 0.75 nA under self-bias conditions, This indicates the presence of a built-in potential. To understand the built-in potential due to the transformation effect, the photocurrent was mapped to different tip biases (V _tip ). In the above measurements, the current was collected during continuous tip scanning from top to bottom, and under conditions of continuous white light irradiation (2 mWcm ^-2 ), V _tip increased from +0.1/-0.1 V to + It varied in steps of 0.1 V up to 0.4/-0.4 V.

These cAFM maps show that the built-in potential is close to the value of Vtip of 0.4 V with the photocurrent removed (see current map corresponding to Vtip = -0.4 V), which is consistent with the bulk measurements (see a in Figure 4). These observations further indicate that the photocurrent varies spatially at the nanoscale (=0.63 nm, i.e., pixel size of the AFM image), thus providing high spatial resolution and making it possible to develop devices accurately even at the nanoscale. .

To obtain a deeper insight into the dynamics of the transformation effect and photoelectric tunability, a controlled mechanical force was applied by an AFM tip (diameter = 30 nm). Priory, the artifacts like surface charge, quantum tunneling, or triboelectrically induced current generation are obtained by producing current maps under a fixed applied force (3 nN), Vtip of 0 V, and dark conditions (including the laser off conditions used in AFM). It was removed by collection.

Figure 5 shows a current map ('a') collected by changing the tip voltage (V _tip ) from +0.1/-0.1 V to +0.4/-0.4 V with a period of 0.1 V under light irradiation conditions, Vtip= Current map of the device collected under zero and dark conditions ('b'), current map collected under self-bias and continuous white light irradiation ('c'), fixed applied force and pulsed light irradiation (P=2 mWcm). ^-2 ) Self-biased instantaneous photoresponse graph ('d') of the device collected from a fixed position using a cAFM tip (diameter = 35 nm) under conditions ('e'), graph showing the force-dependent photocurrent characteristics ('e'), and Shows a graph ('f') measuring the change in photocurrent size according to the applied force.

Referring to Figure 5 a, b, and c, no current signal was observed under Vtip=0 and dark conditions, which means that priory, the artifacts like surface charge, quantum tunneling, or triboelectrically induced current generation are factors related to charge. This indicates that it does not play a dominant role in transmission. On the other hand, a unique and obvious current appeared at V _tip = 0 V under constant white light irradiation (2 mWcm ^-2 ) conditions, confirming the generation and separation of light absorption-induced electron-hole pairs (see c in Figure 5). ) In fact, the point force applied by the AFM tip breaks the symmetry inside the semiconductor by creating a strain gradient, which can cause a transformation effect potential and a resulting current at 0 V. Therefore, it is believed that the potential origin of the photocurrent is the transformation effect polarization field.

As another evidence, as shown in Figure 5d, quantitative photocurrent was measured at a fixed position using a cAFM probe under conditions of pulsed light irradiation (P=0.6 mWcm ^-2 ). Interestingly, from the instantaneous photoresponse (It) measurements at the nanoscale, the current increased rapidly and reached a maximum value of approximately 0.06 nA at V _tip = 0V, confirming that the photocurrent was generated under self-bias conditions. Additionally, the generation of instantaneous photocurrent was highly sensitive to irradiation intensity, confirming that nanoscale current also depends on light absorption. In fact, due to the polarization effect, the electron-hole pairs generated by light were urgently separated to generate photocurrent. This instantaneous photocurrent using a cAFM tip clearly shows that the present invention has an ultra-fast response of milliseconds (ms) and can be applied to device sizes reduced to tens of nanometers to achieve high resolution.

As shown in Figure 5 e, to provide additional direct evidence for the transformation effect induced photocurrent, a controlled force was applied to a fixed point using a cAFM tip, under dark and continuous white light irradiation (P = 2 mW cm Simultaneous photocurrent was measured at V _tip = 0 V under the conditions of ^-2 ). As expected, under dark conditions, the current signal remained at noise level even when the maximum force was applied. On the other hand, a photocurrent appeared under light irradiation conditions, and the size of the photocurrent showed a 1:1 response to the increase/decrease of the applied force (see the green curve in Figure 5e).

The change in average photocurrent as a function of applied force is shown in Figure 5f, showing that it can provide tuning of photoresponse at the nanoscale. The change in photocurrent magnitude with applied force can be explained based on the enhancement of light absorption with reduced bandgap under applied strain conditions. In fact, the band structure can be adjusted with the applied strain along with the generation of transformation-effect polarization, and as a result the overall photovoltaic performance of the device can be effectively tuned. Assuming that photocurrent generation depends on the applied strain, the above results indicate that strain gradient-induced bandgap tuning has a critical effect on photovoltaic performance. In this respect, other tip-induced effects can be ruled out. For example, the change in photocurrent depending on the applied force is reversible, thus ruling out the involvement of any electrochemical process, as expected since V _tip was used as 0V.

Meanwhile, the force-displacement curve was used to calculate the applied strain during the applied point force, and surface topography measurements before and after force application confirmed that the tip did not cause any permanent surface damage. These results confirm that charge transport can be controlled purely by mechanical forces even in nanosized AFM tips.

To prove the feasibility of the present invention for photon detection beyond the basic bandgap, the sensitivity (S) of the device, defined as the ratio of Equation 4 below, was calculated for λ = 1620 nm.

[Formula 4]

Figure 6 is a graph ('a') showing the change in sensitivity (S) of the device to an applied point force for a fixed light irradiation of P=2 mWcm ^-2 and the intensity of the irradiation light for a fixed force of 4 μN. A graph ('b') showing the change in response (R) and sensitivity (D) according to is shown.

As shown in a of Figure 6, S can be adjusted over a wide range, for P=2 mWcm ^-2 was found to be as high as %. This extremely high sensitivity indicates that results can be accurately collected using the device of the present invention.

Other critical parameters to determine the performance of the proposed photovoltaic device are responsivity (R) and sensitivity (D). Assuming that the main contributor to the dark current is due to short-circuit noise, D can be calculated as Equation 5 below:

[Formula 5]

(q represents electrical charge)

In Equation 5, R is (P represents the irradiation intensity of light, and A is the effective irradiation area ( ) can be defined as). (i.e., the average photocurrent measured during light-off conditions during the It measurement); After substitution of appropriate parameters such as etc., the values of R and D measured under self-bias conditions (0V) are 96 mAW ^-1 and were reached, respectively, indicating excellent feasibility of the present invention. In fact, these results demonstrate that the present invention can be applied from nanoscale to microscale, and as a result, major issues related to currently used expensive materials such as InGaAs, InP and other materials can be solved by applying transformation effect. .

Although the present invention has been described above with reference to preferred embodiments, those skilled in the art may make various modifications and changes to the present invention without departing from the spirit and scope of the present invention as set forth in the following patent claims. You will understand that it is possible.

100a, 100b, 200: optical sensor 110a, 100b, 210: light source
120a, 120b, 220: Sensing element 130a, 130b, 230: Current meter
140a, 140b, 240: substrate

Claims (10)

In an optical sensor that detects the presence or movement of an object,
a light source that irradiates light in the direction of the target;
a sensing element that generates a photocurrent by receiving light reflected by the target or light transmitted through the target; and
It includes a current meter that measures the photocurrent,
The sensing element is,
A dielectric thin film formed of a dielectric material having a centrosymmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region;
an electrode disposed on one surface of the dielectric thin film, formed of a transparent conductive material that transmits light in the infrared or visible light region, and electrically connected to the current meter; and
It includes a local force applicator that applies a local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film,
The light source irradiates light containing infrared wavelengths,
Characterized in that the dielectric thin film in which the strain is caused absorbs light having an energy less than the fundamental band gap and generates the photocurrent.
Optical sensor. delete According to paragraph 1,
An optical sensor, wherein the dielectric thin film is formed of a semiconductor material with a fundamental band gap of 1 to 3 eV. According to paragraph 1,
The optical sensor, wherein the local force applicator includes a pointed tip whose tip has a spherical or hemispherical shape. According to paragraph 1,
The electrode includes a conductive metal nanowire electrode, a conductive metal electrode with a mesh structure, a conductive carbon material electrode, a transparent conductive oxide electrode, or a transparent conductive polymer electrode,
An optical sensor, characterized in that a Schottky barrier is formed at the interface between the electrode and the dielectric thin film. According to clause 5,
The electrode includes an opening exposing a portion of the surface of the dielectric thin film,
The local force applicator is characterized in that the local force applicator applies a local force to the surface of the dielectric thin film through the opening. A dielectric thin film formed of a dielectric material having a centrosymmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region; an electrode disposed on one surface of the dielectric thin film and formed of a transparent conductive material capable of transmitting light in the infrared region; and a local force applicator that applies a local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film.
a light source that irradiates light in the direction of the sensing element; and
A current meter electrically connected to the electrode and measuring the photocurrent formed in the dielectric thin film by the light,
The light source irradiates light containing infrared wavelengths,
Characterized in that the strain-induced dielectric thin film absorbs light of the infrared wavelength having an energy smaller than the fundamental bandgap to generate the photocurrent.
Optical sensor. In clause 7,
An optical sensor, wherein the dielectric thin film is formed of a semiconductor material with a fundamental band gap of 1 to 3 eV. delete In a bio-diagnostic device for diagnosing the health condition of a human or animal,
a light source that irradiates light toward the human body or animal;
an array of a plurality of sensing elements each receiving light reflected by the human body or animal or light transmitted through the human body or animal and generating a photocurrent; and
A current meter that measures photocurrents generated by the sensing elements,
Each of the above sensing elements,
A dielectric thin film formed of a dielectric material having a centrosymmetric crystal structure and a fundamental bandgap corresponding to a wavelength in the visible or ultraviolet region;
an electrode disposed on one surface of the dielectric thin film, formed of a transparent conductive material that transmits light in the infrared or visible light region, and electrically connected to the current meter; and
It includes a local force applicator that applies a local force to the surface of the dielectric thin film to cause local non-uniform strain inside the dielectric thin film;
The light source irradiates light containing infrared wavelengths,
A bio diagnostic device, wherein the strain-induced dielectric thin film absorbs light of the infrared wavelength having an energy smaller than the fundamental band gap and generates the photocurrent.