CN106872052A - A kind of wide spectrum pyroelectric detector absorbing coatings structure and preparation method thereof - Google Patents

Abstract

The invention discloses a wide-spectrum pyroelectric detector absorption film system structure and a preparation method thereof, belonging to the field of infrared absorption layers of pyroelectric detectors, and solves the problem of poor adhesion between porous materials and substrates in the prior art and can only be used alone Problems with being used as an absorbent layer. The film structure is prepared on the top layer of the sensitive unit of the pyroelectric detector, including three layers of metal film, the bottom metal film has low porosity and high density, and can maintain good adhesion with the substrate, and the middle layer of metal film serves as a transition Layer, the porosity is increased, the density is reduced, and the top metal film is a loose layer, which can effectively enhance the infrared absorption rate. The prepared metal absorbing layer can be used as the absorbing layer and the upper electrode of the detector at the same time, which greatly simplifies the preparation process, saves costs, improves process compatibility, and provides strong support for the development of high-performance pyroelectric detectors.

Description

A wide-spectrum pyroelectric detector absorbing film structure and its preparation method

technical field

The invention relates to the technical field of infrared absorbing layers of pyroelectric detectors, in particular to a wide-spectrum pyroelectric detector absorbing film structure and a preparation method thereof.

Background technique

Pyroelectric detector is a kind of infrared radiation detection device, which is prepared by utilizing the characteristic of spontaneous polarization of pyroelectric body changing with temperature. Compared with other detectors, it not only maintains the advantages of thermal detectors working in the room temperature band, but also can withstand large radiation power, have a higher detection rate in a wide temperature and frequency range, and have a smaller time constant Features. Pyroelectric detectors are widely used in the fields of national defense, industry, medicine and scientific research, such as intrusion alarm, security monitoring, fire alarm, industrial production monitoring, aircraft and vehicle auxiliary driving, medical diagnosis and many other aspects.

The detectability is the main index to measure the performance of the pyroelectric detector, and increasing the absorption coefficient is the direct way to improve the detectability of the detector. Studies have found that pyroelectric materials themselves have high reflectivity in the far-infrared band. Especially in the 11-20μm band, the reflectivity is as high as 85% (V.Norkus, etc, "A 256pixel pyroelectric linear array with new black coating", Proc.of SPIE, vol.8012, pp.80123V, 2011). Increasing the thickness of the sensing element can reduce the reflectivity to a certain extent, but it will affect the pyroelectric coefficient of the material. In order to effectively absorb thermal radiation and improve the responsivity of the device, it is necessary to cover an absorbing layer or an anti-reflection layer on the surface of the sensitive element. It is required that the infrared absorbing layer has low reflectivity and good adhesion to the underlying material.

At present, the commonly used infrared radiation absorbing layer materials mainly include: ultra-thin metal film, organic black body, porous black metal, etc. Among these substances, the ultra-thin metal film has relatively low reflectivity and high thermal conductivity, but the theoretical limit value of its absorptivity is low. Black resin has a high infrared absorption rate, but is poorly compatible with the device process, and has a large thermal resistance, which may hinder the transmission of heat to sensitive films. Porous black gold has low reflectivity and high broad-spectrum absorption characteristics, but it has weak adhesion and is easy to break. In addition, some literatures reported that a graded-index antireflection layer was etched on the surface of the sensitive material lithium tantalate (LiTaO ₃ ) (A.Finn, etc., “Microstructured surfaces on LiTaO ₃ -based pyroelectric infrared detectors”, IEEE Sensors Journal , vol.11, pp.2204, 2011), based on the anti-reflection layer structure, the absorption rate is significantly improved, but this method changes the surface morphology of sensitive materials, which affects the response characteristics of the device to a certain extent.

Contents of the invention

The technical problem to be solved by the present invention is: how to provide a film structure that realizes wide-spectrum infrared absorption, which can effectively enhance the absorption rate of infrared radiation, and provide strong support for the development of high-performance pyroelectric detectors.

The technical solution of the present invention is: a wide-spectrum pyroelectric detector absorbing film structure, the film structure is located on the top layer of the sensitive unit of the pyroelectric detector, the film structure includes a bottom metal film, a middle layer metal film and The porosity of the top metal film, the bottom metal film, the middle metal film, and the top metal film increases sequentially.

Further, the materials of the bottom metal film, the middle metal film and the top metal film are black gold, bismuth, aluminum, titanium, nickel, chromium or alloys of the above metals.

Further, the infrared absorption rate of the film structure in the 1-20 μm band is better than 60%.

Further, the porosity of the bottom metal film is 15-20%, the porosity of the middle metal film is 30-35%, and the porosity of the top metal film is 45-50%.

Further, the thickness of the bottom metal film is 8-12 nm, the thickness of the middle metal film is 10-15 nm, and the thickness of the top metal film is 10-15 nm.

A method for preparing a wide-spectrum pyroelectric detector absorbing film structure, comprising the following steps:

(1) Prepare a densified underlying metal film by magnetron sputtering on the top layer of the pyroelectric sensitive unit;

(2) adopt magnetron sputtering method to prepare comparatively loose middle layer metal film on the densified bottom metal film of step (1) gained;

(3) Prepare a loose top layer metal film on the middle layer metal film obtained in step (2) by evaporation or magnetron sputtering.

Further, the specific steps of step (1) are: using magnetron sputtering to prepare the underlying metal film, using bismuth, aluminum, titanium, nickel, chromium or their alloys as materials, the working pressure is controlled at 4-6Pa, sputtering The electric current is 0.4-0.6A, and at the same time, the porosity of the film is controlled in the range of 15-20%, and the film thickness is in the range of 8-12nm.

Further, the specific steps of step (2) are: using magnetron sputtering method to prepare the middle layer metal film, using bismuth, aluminum, titanium, nickel, chromium or their alloys as materials, the working pressure is controlled at 8-10Pa, sputtering The range of the jet current is 0.2-0.3A, and the porosity of the film is controlled at 30-35%, and the film thickness is at 10-15nm.

Further, the specific steps of step (3) are: using magnetron sputtering to prepare the top metal thin film, using bismuth, aluminum, titanium, nickel, chromium or their alloys as materials, the process pressure is 12-14Pa, the sputtering current 0.1A, while controlling the porosity of the film in the range of 45-50%, and the film thickness in the range of 10-15nm.

Further, the specific steps of step (3) are: adopt the evaporation method to prepare the top metal thin film, use black gold, bismuth, aluminum, titanium, nickel, chromium or their alloys as materials, adjust the N pressure to _20Pa , control the film thickness to a low At 20 nm, a loose porous metal layer is formed.

Compared with the prior art, the present invention has the following beneficial effects:

The bottom metal thin film of the prepared membrane structure of the present invention has high density and maintains good adhesion with the sensitive layer, and the top layer metal thin film is loose and porous and effectively enhances the infrared absorptivity. The prepared metal absorbing layer can be used as the absorbing layer and the upper electrode of the detector at the same time, which greatly simplifies the preparation process, saves costs, improves process compatibility, and provides strong support for the development of high-performance pyroelectric detectors.

Description of drawings

Fig. 1 is a schematic diagram of a simple preparation process of the film structure of the present invention;

Fig. 2 is the structural representation of the membrane system structure that the present invention prepares;

The reference signs in the figure are: 1. Pyroelectric sensitive unit, 2. Bottom metal film, 3. Middle metal film, 4. Top metal film, 5. Lower electrode.

detailed description

A wide-spectrum pyroelectric detector absorbing film structure, the film structure is located on the top layer of the sensitive unit of the pyroelectric detector, including the bottom metal film, the middle layer metal film and the top layer metal film, the bottom metal film, the middle layer metal film The porosity of the film and the top metal film gradually increases. The preparation process is shown in Figure 1.

The underlying metal thin film prepared on the substrate requires high density and low porosity to achieve good adhesion between the absorbing layer and the substrate. The metal material can be bismuth, aluminum, titanium, nickel, chromium or their alloy films prepared by magnetron sputtering equipment. The density of the material is adjusted by the gas pressure and the sputtering current. The reduction of the gas pressure and the increase of the current will weaken the atomic scattering effect and increase the kinetic energy of the sputtered atoms, which is beneficial to the densification of the microstructure of the film. Therefore, when preparing the bottom metal thin film, the working pressure should be controlled at 4-6Pa, and the sputtering current should be 0.4-0.6A. The porosity is controlled in the range of 15-20%, and the film thickness is controlled in the range of 8-12nm, so as to reduce the influence on the heat capacity of the detector.

The metal thin film in the middle layer is a transition layer, which can appropriately increase the porosity and porosity. The metal material of this layer can be bismuth, aluminum, titanium, nickel, chromium or their alloy films prepared by magnetron sputtering equipment. By appropriately increasing the gas pressure and reducing the sputtering current, the densification of the thin film structure is reduced, and the porosity is controlled within a range of 30-35%. The working pressure needs to be controlled at 8-10Pa, and the sputtering current range is 0.2-0.3A. At the same time, the film thickness range is controlled within 10-15nm to reduce the influence on the heat capacity of the detector.

The top metal film is required to be loose and porous to effectively enhance the infrared absorption rate. The metal material can be bismuth, aluminum, titanium, nickel, chromium or their alloy films prepared by magnetron sputtering equipment. By adopting Ar plasma sputtering in a high-pressure environment and using low sputtering current, the atomic scattering effect is effectively enhanced and the atomic kinetic energy is reduced to form a loose porous metal layer structure similar to black gold to achieve broad-spectrum absorption of infrared radiation. The range of the porosity is controlled to be 45-50%, and the film thickness is controlled to be in the range of 10-15nm, so as to reduce the influence on the heat capacity of the detector. The metal absorption layer on the top layer can also be black gold, bismuth, aluminum, titanium, or an alloy thin film prepared by evaporation, such as NiCr. The metal thin film prepared by the high-pressure _N2 environment is more porous than the metal thin film prepared by the sputtering method, which can further improve the infrared absorption rate.

The present invention will be further described below by embodiment:

Example 1

As shown in Figure 2, a wide-spectrum pyroelectric detector absorbing film structure includes _three layers of metal thin films with gradually increasing porosity. Expand.

The pre-preparation process of LiTaO ₃ crystal slices is: preparing the lower electrode 5 on the LiTaO ₃ wafer; thinning the LiTaO ₃ wafer 4 by grinding and polishing to form the pyroelectric sensitive unit 1 .

LiTaO ₃ crystal thin slices were cleaned and photolithographically patterned on the upper surface. The underlying nickel-chromium alloy film is prepared by magnetron sputtering technology as the underlying metal film 2, the process pressure is adjusted to 4Pa, the sputtering current is 0.6A, and a dense nickel-chromium metal layer is obtained. The porosity range is controlled at 15%, and the thickness range is controlled. at 10nm.

The metal film 3 in the middle layer is prepared by magnetron sputtering technology, which is a nickel-chromium alloy film. The process pressure is adjusted to 8Pa, the sputtering current is 0.4A, the porosity range is controlled at 30%, and the thickness range is controlled at 15nm.

The top metal film 4 is prepared by magnetron sputtering technology, which is a nickel-chromium alloy film. The process pressure is adjusted to 12Pa, the sputtering current is 0.3A, the porosity range is controlled at 50%, and the thickness range is controlled at 15nm to obtain a very loose porous Shaped metal layer, and then floating glue cleaning.

The infrared absorbing layer for wide-spectrum pyroelectric detectors is obtained. According to the sequence of incident radiation, from top to bottom, it is a loose porous nickel-chromium metal layer, a nickel-chromium metal transition layer and a dense nickel-chromium metal layer.

Example 2

As shown in Figure 2, a wide-spectrum pyroelectric detector absorbing film structure includes _three layers of metal thin films with gradually increasing porosity. Expand.

The pre-preparation process of LiTaO ₃ crystal flakes is: preparing the lower electrode 5 on the lithium tantalate wafer; thinning the lithium tantalate wafer by grinding and polishing to form the pyroelectric sensitive unit 1 .

LiTaO ₃ crystal thin slices were cleaned and photolithographically patterned on the upper surface. The underlying metal film 2 is prepared by magnetron sputtering technology, which is a bismuth metal film. The process pressure is adjusted to 5Pa, and the sputtering current is 0.7A to obtain a dense bismuth metal layer. The porosity range is controlled at 20%, and the thickness range is controlled at 10nm. .

The middle layer metal thin film 3 is prepared by magnetron sputtering technology, which is a bismuth metal thin film. The process pressure is adjusted to 7Pa, the sputtering current is 0.5A, the porosity range is controlled at 30%, and the thickness range is controlled at 15nm.

The top metal thin film 4 is prepared by evaporation method, which is a bismuth metal thin film. The _N2 pressure is adjusted to 20Pa, the porosity range is controlled at 45%, and the film thickness is controlled to be less than 20nm to form a loose porous bismuth metal layer, and then the floating glue is cleaned.

The infrared absorbing layer for wide-spectrum pyroelectric detectors is obtained. According to the order of incident radiation, from top to bottom, the top layer is loose and porous bismuth metal film, the middle layer is bismuth metal film and the bottom layer is dense bismuth metal film.

Claims (10)

1. A wide-spectrum pyroelectric detector absorption film structure, the film structure is located on the top layer of the pyroelectric detector sensitive unit, it is characterized in that, the film structure comprises bottom metal thin film, middle layer metal thin film and top layer The porosity of the metal film, the bottom metal film, the middle layer metal film, and the top layer metal film increases sequentially. 2. a kind of wide-spectrum pyroelectric detector absorption film system structure according to claim 1 is characterized in that, the material of bottom metal film, middle layer metal film and top layer metal film is black gold, bismuth, aluminum, titanium, Nickel, chromium or alloys of the above metals. 3 . The wide-spectrum pyroelectric detector absorbing film structure according to claim 1 , wherein the film structure has an infrared absorption rate better than 60% in the 1-20 μm band. 4 . 4. A kind of wide-spectrum pyroelectric detector absorption film system structure according to claim 1, is characterized in that, the porosity of bottom metal film is 15～20%, the porosity of middle layer metal film is 30～35%. %, the porosity of the top metal film is 45-50%. 5. A kind of wide-spectrum pyroelectric detector absorption film system structure according to claim 1, it is characterized in that, the thickness of bottom layer metal film is 8～12nm, the thickness of middle layer metal film is 10～15nm, top layer metal film The thickness of the film is 10-15 nm. 6. The preparation method of a kind of wide-spectrum pyroelectric detector absorbing film system structure according to any one of claims 1 to 5, characterized in that it comprises the following steps: (1) Prepare a densified underlying metal film by magnetron sputtering on the top layer of the pyroelectric sensitive unit; (2) adopt magnetron sputtering method to prepare comparatively loose middle layer metal film on the densified bottom metal film of step (1) gained; (3) Prepare a loose top layer metal film on the middle layer metal film obtained in step (2) by evaporation or magnetron sputtering. 7. the preparation method of a kind of broad-spectrum pyroelectric detector absorption film system structure according to claim 6 is characterized in that, the concrete steps of step (1) are: adopt magnetron sputtering method to prepare bottom metal thin film, Bismuth, aluminum, titanium, nickel, chromium or their alloys are used as materials, the working pressure is controlled at 4-6Pa, the sputtering current is 0.4-0.6A, and the porosity of the film is controlled at 15-20%, and the film thickness ranges at 8-12nm. 8. the preparation method of a kind of wide-spectrum pyroelectric detector absorbing film system structure according to claim 6 is characterized in that, the concrete step of step (2) is: adopt magnetron sputtering method to prepare interlayer metal thin film , with bismuth, aluminum, titanium, nickel, chromium or their alloys as materials, the working pressure is controlled at 8-10Pa, the sputtering current range is 0.2-0.3A, and the porosity of the film is controlled at 30-35%. The range is 10-15nm. 9. the preparation method of a kind of broad-spectrum pyroelectric detector absorbing film system structure according to claim 6, is characterized in that, the concrete steps of step (3) are: adopt magnetron sputtering method to prepare top metal thin film, Bismuth, aluminum, titanium, nickel, chromium or their alloys are used as materials, the process pressure is 12-14Pa, the sputtering current is 0.1A, and the porosity of the film is controlled at 45-50%, and the film thickness is 10-15nm . 10. the preparation method of a kind of broad-spectrum pyroelectric detector absorbing film system structure according to claim 6 is characterized in that, the concrete step of step (3) is: adopt evaporation method to prepare top metal film, with black gold, Bismuth, aluminum, titanium, nickel, chromium or their alloys are used as materials, the _N2 pressure is adjusted to 20Pa, and the film thickness is controlled to be less than 20nm to form a loose porous metal layer with a porosity ranging from 45% to 50%.