Browse Theses

Power consumption has become the key constraint in electronics design, since the MOSFET threshold voltage (Vth) and hence the supply voltage (Vdd) can no longer be scaled. This trend calls for new device concepts such as Spintronic devices that are fundamentally different from CMOS. However, the MOSFET-type Spintronics transistor has not been demonstrated yet due to the technical difficulties in injecting, transporting and detecting spin information. In this work, I present an alternative Spintronics logic device, Magnetic Coupled Spin Torque Device (MCSTD), which is free from spin-injection, transport and detection problems. It leverages spin-torque transfer effect and magnetic dipole coupling between spin-torque devices to modulate its magnetization reversal energy barrier. Its device switching speed, signal inversion and signal level restoration capabilities will be discussed. For device-to-device level spin communication, MCSTD uses a novel interconnection technique that efficiently converts spin (or magneto-resistance) information to current amplitude difference information, which is then converted back to spin information at the subsequent gates. In micro-magnetic simulations, MCSTD-based NAND, NOR, XOR gates and a three-stage ring oscillator have been demonstrated to estimate realistic device speed and power consumption. The fabrication of 20nm gap MCSTDs has been successfully completed and demonstrated the input dependent switching voltage modulation, i.e., switching voltage of MCSTD gate depends on the magnetic orientations of the input spin-torque devices. The amount of voltage shifts ranged between 40~300mV, which is well above thermal fluctuations. Non-volatility in logic device such as MCSTD opens up very unique potential applications in future power management techniques and smart sensor technologies. For example, MCSTDs can replace SRAMs and pass gate transistors in reconfigurable logics such as Field Programmable Gate Array (FPGA). Instant-on/off nature of MCSTD enables low overhead system-level power gating scheme for embedded devices. Also, MCSTD can be used as a magnetic sensor with in-situ logic operations for error-resilient DNA microarray sensors.This work also explored other disruptive low-power device and system solutions such as Graphene nano-ribbon /Carbon nanotube based heterojunction Tunneling FET (Chap.8) and Error Resilient System Architecture for Probabilistic Applications (Chap.9).