Showing papers by "Veena Misra published in 2020"

Engineering a Unified Dielectric Solution for AlGaN/GaN MOS-HFET Gate and Access Regions

Abstract: Typically GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) have used two separate dielectrics for the gate and access regions. However, as this article shows, with proper gate-stack engineering, a unified dielectric solution can be achieved for the transistor. HfO2 dielectrics were deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O3). It was found that MOS-HFETs with O3 oxidant yielded lower threshold voltage ( ${V}_{\text {TH}}$ ) shifts, higher maximum drain current ( ${I}_{\text {DS,max}}$ ) of 340 mA/mm, 20% lower ON-resistance ( ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ ), higher peak transconductance at 112.66 mS/mm, lower hysteresis, and lower gate leakage ( ${5.4} \times {10}^{-{6}}$ A/cm2) compared to water oxidant based MOS-HFETs with ${I}_{\text {DS},\text {max}}$ of 240 mA/mm, 81.38 mS/mm peak transconductance, and ${1.7} \times {10}^{-{4}}$ A/cm2 gate leakage. DC/RF dispersion tests showed MOS-HFETs with O3 oxidant had ~200 $\times $ better current collapse recovery. Temperature characterization and reliability test results, such as high-temperature reverse bias (HTRB), are published for the first time on ALD-HfO2/AlGaN/GaN MOS-HFETs using tetrakis(dimethylamino)hafnium (TDMAH) and O3 precursor. Using an ozone oxidant provided more stability (i.e., less variability in ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ and ${V}_{\text {TH}}$ ) as a function of temperature. Finally, when devices were electrically stressed in the OFF-state, the HTRB test showed minimal ${V}_{\text {TH}}$ drift ( ${V}_{\text {TH}}$ drift (2.5 V) in the case of H2O oxidant.

A Pipeline for Adaptive Filtering and Transformation of Noisy Left-Arm ECG to Its Surrogate Chest Signal

Abstract: The performance of a low-power single-lead armband in generating electrocardiogram (ECG) signals from the chest and left arm was validated against a BIOPAC MP160 benchtop system in real-time. The filtering performance of three adaptive filtering algorithms, namely least mean squares (LMS), recursive least squares (RLS), and extended kernel RLS (EKRLS) in removing white (W), power line interference (PLI), electrode movement (EM), muscle artifact (MA), and baseline wandering (BLW) noises from the chest and left-arm ECG was evaluated with respect to the mean squared error (MSE). Filter parameters of the used algorithms were adjusted to ensure optimal filtering performance. LMS was found to be the most effective adaptive filtering algorithm in removing all noises with minimum MSE. However, for removing PLI with a maximal signal-to-noise ratio (SNR), RLS showed lower MSE values than LMS when the step size was set to 1 × 10−5. We proposed a transformation framework to convert the denoised left-arm and chest ECG signals to their low-MSE and high-SNR surrogate chest signals. With wide applications in wearable technologies, the proposed pipeline was found to be capable of establishing a baseline for comparing left-arm signals with original chest signals, getting one step closer to making use of the left-arm ECG in clinical cardiac evaluations.

An 88.6nW ozone pollutant sensing interface IC with a 159 dB dynamic range

Abstract: This paper presents a low power resistive sensor interface IC designed at 0.6V for ozone pollutant sensing. The large resistance range of gas sensors poses challenges in designing a low power sensor interface. Exiting architectures are insufficient for achieving a high dynamic range while enabling low VDD operation, resulting in high power consumption regardless of the adopted architecture. We present an adaptive architecture that provides baseline resistance cancellation and dynamic current control to enable low VDD operation while maintaining a dynamic range of 159dB across 20kΩ-1MΩ. The sensor interface IC is fabricated in a 65nm bulk CMOS process and consumes 88.6nW of power which is 300x lower than the state-of-art. The full system power ranges between 116 nW - 1.09 μW which includes the proposed sensor interface IC, analog to digital converter and peripheral circuits. The sensor interface's performance was verified using custom resistive metal-oxide sensors for ozone concentrations from 50 ppb to 900 ppb.

Preliminary Assessment of Human Biological Responses to Low-level Ozone

Abstract: Multi-modal wearable sensors monitoring physiology and environment simultaneously would offer a great promise to manage respiratory health, especially for asthmatic patients. In this study, we present a preliminary investigation of the correlation between ozone exposure, heart rate, heart rate variability, and lung function. As the first step, we tested the effect of low-level ozone exposure in a sample size of four healthy individuals. Test subjects underwent controlled exposure from 0.06 to 0.08 ppm of ozone and filtered air on two separate exposure days. Our results indicate an increment in mean heart rate in three out of four test subjects when exposed to ozone. We have also observed that changes in mean heart rate has a positive correlation with changes in lung function and a negative correlation with changes in neutrophil count. These results provide a baseline understanding of healthy subjects as a control group.