Shruti Patil

Direct communication between magnetic tunnel junctions for nonvolatile logic fan-out architecture

We experimentally demonstrated a magnetic tunnel junction (MTJ) based circuit that allows direct communication between elements without intermediate sensing amplifiers. The input of the circuit consists of three MTJs connected in parallel. The direct communication is realized by connecting the output in series with the input and applying voltage across the series connections. Combining the circuit with complementary metal oxide semiconductor current mirrors allows for fan-out to multiple outputs. The change in resistance at the input resulted in a voltage swing across the output of 150–200 mV for the closest input states which is sufficient to realize all of the Boolean primitives.

Spintronic logic gates for spintronic data using magnetic tunnel junctions

The emerging field of spintronics is undergoing exciting developments with the advances recently seen in spintronic devices, such as magnetic tunnel junctions (MTJs). While they make excellent memory devices, recently they have also been used to accomplish logic functions. The properties of MTJs are greatly different from those of electronic devices like CMOS semiconductors. This makes it challenging to design circuits that can efficiently leverage the spintronic capabilities. The current approaches to achieving logic functionality with MTJs include designing an integrated CMOS and MTJ circuit, where CMOS devices are used for implementing the required intermediate read and write circuitry. The problem with this approach is that such intermediate circuitry adds overheads of area, delay and power consumption to the logic circuit. In this paper, we present a circuit to accomplish logic operations using MTJs on data that is stored in other MTJs, without an intermediate electronic circuitry. This thus reduces the performance overheads of the spintronic circuit while also simplifying fabrication. With this circuit, we discuss the notion of performing logic operations with a non-volatile memory device and compare it with the traditional method of computation with separate logic and memory units. We find that the MTJ-based logic unit has the potential to offer a higher energy-delay efficiency than that of a CMOS-based logic operation on data stored in a separate memory module.

Magnetic Tunnel Junction Logic Architecture for Realization of Simultaneous Computation and Communication

We investigated magnetic tunnel junction (MTJ)-based circuit that allows direct communication between elements without intermediate sensing amplifiers. Two- and three-input circuits that consist of two and three MTJs connected in parallel, respectively, were fabricated and are compared. The direct communication is realized by connecting the output in series with the input and applying voltage across the series connections. The logic circuit relies on the fact that a change in resistance at the input modulates the voltage that is needed to supply the critical current for spin-transfer torque switching the output. The change in the resistance at the input resulted in a voltage swing of 50-200 mV and 250-300 mV for the closest input states for the three and two input designs, respectively. The two input logic gate realizes the AND, NAND, NOR, and OR logic functions. The three-input logic function realizes the majority, AND, NAND, NOR, and OR logic operations.

A pure single-walled carbon nanotube thin film based three-terminal microelectromechanical switch

The electrical and physical properties of pure single-walled carbon nanotube thin films deposited through a layer-by-layer-self-assembly process are discussed. The film thickness was proportional to the number of dipping cycles. The film resistivity was estimated as 2.19×10−3 Ω cm after thermal treatment processes were performed. The estimated specific contact resistance to gold electrodes was 6.33×10−9 Ω m2 from contact chain measurements. The fabricated three-terminal microelectromechanical switch using these films functioned as a beam for multiple switching cycles with a 4.5 V pull-in voltage. This switch is believed to be a promising device for low power digital logic applications.

Using Resampling Techniques to Compute Confidence Intervals for the Harmonic Mean of Rate-Based Performance Metrics

Rate-based metrics such as floating point operations per second, instructions per cycle and so forth are commonly used to measure computer performance. In addition to the average or mean performance of the metric, indicating the precision of the mean using confidence intervals helps to make informed decisions and comparisons with the data. In this paper, we discuss the determination of confidence intervals for the harmonic mean of rate-based metrics using two statistical resampling techniques - Jackknife and Bootstrap. We show using Monte Carlo simulations that resampling indeed works as expected, and can be used for generating confidence intervals for harmonic mean.

A programmable and scalable technique to design spintronic logic circuits based on magnetic tunnel junctions

Exciting developments are taking place in the field of spintronics, particularly with the advances in the fabrication and characterization of devices such as Magnetic Tunnel Junctions (MTJ). The distinction of spintronic devices from conventional electronic devices makes it challenging to design efficient, scalable and low power logic circuits with MTJs. We propose a programmable and scalable technique to design MTJ-based logic circuits that are capable of implementing any 2-input logic truth table. We present the energy-delay trade-offs of this design with respect to circuit parameters. We also demonstrate that this circuit can be scaled to a 6-input logic function without incurring an increase in the energy consumption.

A three-terminal single-walled carbon nanotube thin film MEMS switch for digital logic applications

An all single-walled carbon nanotube film was deposited through layer-by-layer self-assembly without use of a copolymer, resulting in 75% reduction of resistivity compared to previous composite films made with copolymer. The deposited film thickness could be well controlled by changing the number of dipping cycles. Moreover, a 3-terminal electromechanical switch built with this thin film behaved like a NAND gate. The on/off ratio of the device and the electrical properties of the film were dramatically improved through thermal treatments.