Sameer Sonkusale

High speed terahertz modulation from metamaterials with embedded high electron mobility transistors.

We present a computational and experimental study of a novel terahertz (THz) device resulting from hybridization of metamaterials with pseudomorphic high electron mobility transistors (HEMTs), fabricated in a commercial gallium arsenide (GaAs) process. Monolithic integration of transistors into each unit cell permits modulation at the metamaterial resonant frequency of 0.46 THz. Characterization is performed using a THz time-domain spectrometer (THz-TDS) and we demonstrate switching values over 30%, and THz modulation at frequencies up to 10 megahertz (MHz). Our results demonstrate the viability of incorporating metamaterials into mature semiconductor technologies and establish a new path toward achieving electrically tunable THz devices.

An Adaptive Resolution Asynchronous ADC Architecture for Data Compression in Energy Constrained Sensing Applications

An adaptive resolution (AR) asynchronous analog-to-digital converter (ADC) architecture is presented. Data compression is achieved by the inherent signal dependent sampling rate of the asynchronous architecture. An AR algorithm automatically varies the ADC quantizer resolution based on the rate of change of the input. This overcomes the trade-off between dynamic range and input bandwidth typically seen in asynchronous ADCs. A prototype ADC fabricated in a 0.18 μm CMOS technology, and utilizing the subthreshold region of operation, achieves an equivalent maximum sampling rate of 50 kS/s, an SNDR of 43.2 dB, and consumes 25 μW from a 0.7 V supply. The ADC is also shown to provide data compression for accelerometer applications as a proof of concept demonstration.

Single and dual band 77/95/110 GHz metamaterial absorbers on flexible polyimide substrate

Ultra thin millimeter-wave absorbers on flexible polyimide substrate utilizing metamaterials are implemented for single and dual frequency bands in an emerging frequency spectrum of 77, 95, and 110 GHz. The dual band absorber is designed using a novel approach of imbedding high frequency resonator inside low frequency resonator capable of absorbing electromagnetic energy at both 77 and 110 GHz bands simultaneously. The total thickness of the absorber is just 126 μm (almost 1/20th of the wavelength). Measured peak absorptions for single frequency absorbers are 92, 94, and 99% at 77.2, 94.8, and 109.5 GHz, respectively, and for dual band absorber 92% at 77 GHz and 94% at 109.8 GHz.

A 60-dB Gain OTA Operating at 0.25-V Power Supply in 130-nm Digital CMOS Process

This paper presents a 60-dB gain bulk-driven Miller OTA operating at 0.25-V power supply in the 130-nm digital CMOS process. The amplifier operates in the weak-inversion region with input bulk-driven differential pair sporting positive feedback source degeneration for transconductance enhancement. In addition, the distributed layout configuration is used for all the transistors to mitigate the effect of halo implants for higher output impedance. Combining these two approaches, we experimentally demonstrate a high gain of over 60-dB with just 18-nW power consumption from 0.25-V power supply. The use of enhanced bulk-driven differential pair and distributed layout can help overcome some of the constraints imposed by nanometer CMOS process for high performance analog circuits in weak inversion region.

Biodegradable Nanofibrous Polymeric Substrates for Generating Elastic and Flexible Electronics

Biodegradable nanofibrous polymeric substrates are used to fabricate suturable, elastic, and flexible electronics and sensors. The fibrous microstructure of the substrate makes it permeable to gas and liquid and facilitates the patterning process. As a proof-of-principle, temperature and strain sensors are fabricated on this elastic substrate and tested in vitro. The proposed system can be implemented in the field of bioresorbable electronics and the emerging area of smart wound dressings.

Microwave diode switchable metamaterial reflector/absorber

We embed diodes as active circuit elements within a metamaterial to implement a switchable metamaterial reflector/absorber at microwave frequencies. Diodes are placed in series with the unit cells of the metamaterial array. This results in just a pair of control lines to actively tune all the diodes in a metamaterial. Diodes can be tuned on and off to switch the function of the metamaterial between a perfect absorber and a reflector. The design, simulation, and experimental results of a switchable reflector/absorber in 2–6 GHz range are presented.

Metamaterials on parylene thin film substrates: Design, fabrication, and characterization at terahertz frequency

We design, fabricate, and characterize terahertz (THz) resonant metamaterials on parylene free-standing thin film substrates. Several different metamaterials are investigated and our results show strong electromagnetic responses at THz frequencies ranging from 500 GHz to 2.5 THz. The complex frequency dependent dielectric properties of parylene are determined from inversion of reflection and transmission data, thus indicating that parylene is an ideal low loss substrate or coating material. The biostable and biocompatible properties of parylene coupled with the multifunctional exotic properties of metamaterials indicate great potential for medical purposes such as THz imaging for skin cancer detection.

A Novel BPSK Demodulator for Biological Implants

A novel binary phase-shift keying (BPSK) demodulator architecture is presented. The design employs a phase frequency detector based phase-locked loop allowing for robust performance compared to prior art. Two different circuit implementations for the novel demodulator architecture are proposed. Based on theoretical analysis, the maximum data rate of the demodulator is derived to be 1/8th of the carrier frequency. For experimental validation, a prototype was implemented for a 13.56-MHz BPSK demodulator in a 0.5-mum CMOS technology. The circuit occupies 1 mm2 chip area and consumes 3-mW power without any circuit optimization and can be further improved. Bit-error rate measurements have also been presented for a 20-kbs data rate.

A toolkit of thread-based microfluidics, sensors, and electronics for 3D tissue embedding for medical diagnostics

Threads, traditionally used in the apparel industry, have recently emerged as a promising material for the creation of tissue constructs and biomedical implants for organ replacement and repair. The wicking property and flexibility of threads also make them promising candidates for the creation of three-dimensional (3D) microfluidic circuits. In this paper, we report on thread-based microfluidic networks that interface intimately with biological tissues in three dimensions. We have also developed a suite of physical and chemical sensors integrated with microfluidic networks to monitor physiochemical tissue properties, all made from thread, for direct integration with tissues toward the realization of a thread-based diagnostic device (TDD) platform. The physical and chemical sensors are fabricated from nanomaterial-infused conductive threads and are connected to electronic circuitry using thread-based flexible interconnects for readout, signal conditioning, and wireless transmission. To demonstrate the suite of integrated sensors, we utilized TDD platforms to measure strain, as well as gastric and subcutaneous pH in vitro and in vivo.

CMOS Microelectrode Array for Electrochemical Lab-on-a-Chip Applications

Microelectrode arrays (MEAs) offer numerous benefits over macroelectrodes due to their smaller sample size requirement, small form factor, low-power consumption, and higher sensitivity due to increased rates of mass transport. These features make MEAs well suited for microfluidic lab-on-a-chip applications. This paper presents two implementations of MEAs with and without an on chip potentiostat. We first describe an 8times8 array of 6 mum circular microelectrodes with center to center 37 mum spacing fabricated on silicon using conventional microfabrication techniques. Pads are provided for external connections to a potentiostat for electrochemical analysis. The second implementation is an individually addressable 32times32 array of 7 mum square microelectrodes with 37 mum center to center spacing on a CMOS chip with built-in very-large-scale integration potentiostat for electrochemical analysis. The integrated CMOS MEA is post processed at the die level to coat the exposed Al layers with Au. To verify microelectrode array behavior with individual addressability, cyclic voltammetry was performed using a potassium ferricyanide (K3Fe(CN)6) solution.