Browsing by Author "Benedict, Samatha"

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Activate Zeolite Filter: A gas sensor signal stabilization and enhancement
(IEEE, 2019) Benedict, Samatha
In this report, we investigate zeolite as a humidity filter by optimizing its heating temperature providing constant humidity to the gas sensor chip. The metal oxide semiconductor (MOS) based gas sensor signals are prone to humidity and temperature variations which causes difficulty in distinguishing the sensor response. The baseline drift of MOS sensor, their signal stability and repeatability are achieved by heated zeolite filter assembly as part of packaged sensor. The sensor package consists of a sandwich of zeolite powder and nichrome wire, which controls the humidity and temperature of the sensor. With the packaged filter and sensor assembly, the recorded humidity and temperature near the sensor chip are 35±5% RH and 40±5°C when the external humidity and temperature is varying from 30 to 80% RH and 21 to 35°C. NO 2 sensor is investigated with and without the filter for proof of concept to check the sensor stability and repeatability.
Colloidal lithography nanostructured Pd/PdOx core–shell sensor for ppb level H2S detection
(IOP, 2018-04) Benedict, Samatha
In this work we report on plasma oxidation of palladium (Pd) to form reliable palladium/palladium oxide (Pd/PdOx) core–shell sensor for ppb level H2S detection and its performance improvement through nanostructuring using hole-mask colloidal lithography (HCL). The plasma oxidation parameters and the sensor operating conditions are optimized to arrive at a sensor device with high sensitivity and repeatable response for H2S. The plasma oxidized palladium/palladium oxide sensor shows a response of 43.1% at 3 ppm H2S at the optimum operating temperature of 200 °C with response and recovery times of 24 s and 155 s, respectively. The limit of detection (LoD) of the plasma oxidised beam is 10 ppb. We further integrate HCL, a bottom-up and cost-effective process, to create nanodiscs of fixed diameter of 100 nm and varying heights (10, 15 and 20 nm) on 10 nm thin Pd beam which is subsequently plasma oxidized to improve the H2S sensing characteristics. The nanostructured Pd/PdOx sensor with nanodiscs of 100 nm diameter and 10 nm height shows an enhancement in sensing performance by 11.8% at same operating temperature and gas concentration. This nanostructured sensor also shows faster response and recovery times (15 s and 100 s, respectively) compared to the unstructured Pd/PdOx counterpart together with an experimental LoD of 10 ppb and the estimated limit going all the way down to 2 ppb. Material characterization of the fabricated Pd/PdOx sensors is done using UV–vis spectroscopy and x-ray photoemission spectroscopy.
Enhanced sensor life using UV treatment of sulphur poisoned Pt-PtOx
(Elsevier, 2019-04) Benedict, Samatha
In this work,we report a novel method for recovery of sulphur poisoned platinum/platinum oxide (Pt-PtOx) core-shell nanowire sensor using UV irradiation.The optimum core to shell thickness ratio and the operating conditions are the key factors to achieve a high-performance H2S sensor,described in this report.The fabricated core-shell nanowire sensor demonstrated response of 6.4% at 1 ppm H2S with detection limit of 10 ppb at 150 °C operating temperature. The sensor undergoes prominent time-dependent poisoning at H2S exposure of 3 ppm when operated at 150 °C due to sensor surface contamination by sulphur,later confirmed by XPS analysis. Ultraviolet light at two wavelengths, 365 nm, and 248 nm is investigated to recover the poisoned Pt-PtOx surface.UV irradiation at 248 nm for 5 min results in sensor recovery, confirmed by further H2S sensing characterization and XPS studies on the recovered sensor. To the best of our knowledge, this is one of the first reports on UV irradiation for recovery of sulphur poisoned metal-oxide surfaces.
Heterogenous Integration of MEMS Gas Sensor using FOWLP : Personal Environment Monitors
(IEEE, 2020) Benedict, Samatha
The exponentially increasing global population has led to environmental pollution which drastically affects human health; emphasizing the need for personal environmental monitoring. This demands the development of wearable devices capable of sensing the local environment and wirelessly transmitting data to cloud for spatial pollution tracking.In this paper, we have demonstrated the integration of MEMS gas sensors on flexible PDMS substrate using the fan out wafer packaging technique called FlexTrate™. One of the main issues in FOWLP involving the integration of MEMS sensors with a released membrane is the stability of the membrane during the molding process which results in poor yield. We have optimized the process for integrating released MEMS devices by protecting the membrane prior to the molding process and thus improving the stability of the released membranes and improving the yield by >80%. If the membrane is not protected, during curing the cavity which is filled by PDMS leads to membrane cracking due to generation of stresses. Simulation studies on the temperature profile of the microheater after protecting the membrane shows that the power consumption for 300 o C of heater temperature is 0.1W as compared to 0.091W where the PDMS fills the cavity of the membrane, which is <; 10% increase. Thus, this proves that the membrane protection process improves stability without affecting the thermal characteristics of the heater. Furthermore, there is an effort to integrate rechargeable flexible batteries to power the system wirelessly. Adding to this, is the capability of wireless communication achieved by integrating a Bluetooth die in the system to transmit data to a mobile phone.The MEMS sensors along with the other electronic components such as transimpedance amplifiers, analog-to-digital converters and Bluetooth will be integrated on the same PDMS platform with interconnect pitches of 40 μm.
A High Spatial Resolution Surface Electromyography (sEMG) System Using Fan-Out Wafer-Level Packaging on FlexTrate™
(IEEE, 2020) Benedict, Samatha
We demonstrate a fully integrated wireless surface electromyography (sEMG) system using Fan-Out Wafer-Level Packaging on a flexible biocompatible package with two corrugated high conductivity electroplated Cu wiring levels for efficient routing. The assembly has reliable performance under repeated flexing of >3000 times. The advanced Au capped Cu-based sensing electrode array architecture provides a high spatial resolution sEMG measurement with SNR comparable to standard Ag/AgCl electrodes, allowing for muscle activation signals to be recorded and transmitted wirelessly for off-line post processing. The system, which is compatible with our wireless charging system has a small form factor of 65 mm x 40 mm x 1 mm and light weight of <; 5 gm, making sEMG widely available outside the hospital setting.
Low power gas sensor array on flexible acetate substrate
(IOP, 2017-06) Benedict, Samatha
In this paper, we present a novel approach of fabricating a low-cost and low power gas sensor array on flexible acetate sheets for sensing CO, SO2, H2 and NO2 gases. The array has four sensor elements with an integrated microheater which can be individually controlled enabling the monitoring of four gases. The thermal properties of the microheater characterized by IR imaging are presented. The microheater with an active area of 15 µm × 5 µm reaches a temperature of 300 °C, consuming 2 mW power, the lowest reported on flexible substrates. A sensing electrode is patterned on top of the microheater, and a nanogap (100 nm) is created by an electromigration process. This nanogap is bridged by four sensing materials doped with platinum, deposited using a solution dispensing technique. The sensing material characterization is completed using energy dispersive x-ray analysis. The sensing characteristics of ZnO for CO, V2O5 for SO2, SnO2 for H2 and WO3 for NO2 gases are studied at different microheater voltages. The sensing characteristics of ZnO at different bending angles is also studied, which shows that the microheater and the sensing material are intact without any breaking upto a bending angle of 20°. The ZnO CO sensor shows sensitivity of 146.2% at 1 ppm with good selectivity.
Microwave-Synthesized NiO as a Highly Sensitive and Selective Room-Temperature NO2 Sensor
(IOP, 2018-04) Benedict, Samatha
In this work, we report microwave-assisted deposition of NiO for application as room- temperature NO2 sensor. The synthesis conditions are varied to arrive at the optimum film for sensing NO2. The optimum NiO film shows response of 4991% at 3 ppm NO2 at room temperature with short response and recovery times of 30 s and 45 s, respectively. X-ray diffraction reveals the cubic structure of the NiO film with slightly preferred orientation and scanning electron microscopy shows high porosity in the film, both contributing to the enhanced sensing performance. The microwave-synthesized NiO shows an order of magnitude stronger response to NO2 (3 ppm) at room temperature operation than does optimized, DC-reactive-sputtered NiO operating at 175°C. To the best of our knowledge, this is the first report on room temperature detection of NO2 by a microwave-synthesized NiO film. The detection limit of the NiO film is 200 ppb with good selectivity against interfering gases. The sensor demonstrates an ultra-low power consumption of 0.2 μW, making it suitable for solar-powered pollution-monitoring.
Multi-Peaked Velocity Spectrum of a AC-Electric-Field-Induced Electrolytic Flow with Microelectrodes
(Applied Mechanics and Materials, 2012-11) Benedict, Samatha
We study the electrolytic flow in a system of coplanar parallel electrodes subjected to an AC field. The model system has been thoroughly examined numerically for a large range of frequencies of the applied potential where we find a peak in the spectrum of the velocity magnitude at high frequencies along with exhibition of a pronounced peak at lower frequencies. Interestingly the first peak in the velocity spectrum shifts to lower frequencies while the second peak to higher frequencies with increasing distance from the electrode edge which suggests a formation of a non-planar electric double layer structure at higher frequencies.
Nanodisc Decorated W–WO x Suspended Nanowire: A Highly Sensitive and Selective H2S Sensor
(IEEE, 2019-03) Benedict, Samatha
In this paper, we report room temperature synthesis of plasma oxidized, suspended tungsten-tungsten oxide (W-WOx) core-shell nanowire for sensing ppb level H 2 S. The electric field modulation at the W-WOx interface of the core-shell nanowire strongly influences the sensing performance and brings down the operating temperature all the way down to 50 °C, compared to completely oxidized (WO x ) nanowire. The optimum interface ratio (W/WOx) of the nanowire shows response of 90.4% (1 ppm) with six months of response stability and excellent selectivity. The limit of detection of 10 ppb with response and recovery time of 4 and 46 s, respectively, is achieved. To enhance the response further, we utilize nanostructuring on top of nanowire, using nanodiscs of 20, 50, and 100 nm diameter and 10 nm height. The nanowire with nanodiscs of 20 nm diameter shows high repeatable response of 12529% (1 ppm) at 150 °C and fast response and recovery times of 12 and 19 s with detection limit of 0.5 ppb. As we switch from unpatterned to patterned nanowire, the observed change in H 2 S sensing characteristics indicates that the core-shell nanowire behavior makes a transition from p-type to n-type. Extensive material characterization is done using UV-Vis spectroscopy, XPS, and TEM.
Nanowire Impregnated Poly-dimethyl Siloxane for Flexible, Thermally Conductive Fan-Out Wafer-Level Packaging
(IEEE, 2020) Benedict, Samatha
FlexTrate TM , a flexible hybrid electronics (FHE) platform based on fan-out wafer level packaging (FOWLP) has demonstrated low die shift by using room temperature cured poly-dimethyl siloxane (PDMS) as a molding compound. In this paper, we investigate the enhancement of the thermal conductivity in PDMS used in the FlexTrate TM process to allow for better thermal management via microwave welding of commercially available copper nanowires dispersed in an uncured PDMS matrix, followed by a standard curing process. We also evaluate the thermal stability of PDMS, necessary if FlexTrate TM assemblies are to be used in conjunction with commonly used solder reflow processes, and show that PDMS is stable at standard reflow temperatures. Thermal conductivity enhancement using the microwave welding process is shown to be minimal, with a peak enhancement of ~40%.
Plasma Oxidized Suspended Core-Shell Nanostructures for High Performance Metal Oxide Gas sensors
(IEEE, 2019) Benedict, Samatha
We report on the novel technique of creating core-shell metal-metal oxide high performance gas sensors using plasma oxidation of a suspended metal thin film. We demonstrate that this technique is very generic by realizing Pt-PtOx and W-WOx nanostructured sensors. The optimization technique for plasma oxidation is elucidated. We also propose an improvisation technique to create nano discs on top of suspended core-shell metal-metal oxide sensor to further enhance the performance.
Plasma Oxidized W-WOx Sensor for Sub-ppm H2S Detection
(MDPI, 2017-08) Benedict, Samatha
In this work we have fabricated W-WOx core-shell nanowire structure using plasma oxidation, a CMOS compatible process, for sensing H2S gas. For comparison, the sputtered stack structure of W-WOx with different thickness ratios of W to WOx is fabricated and characterized for H2S sensing. The sensor fabricated using plasma oxidation process is found to be significantly better in sensing performance compared to the sensing results obtained from sensor fabricated using sputtering. The response of plasma oxidized sensor is 90.4% for 1 ppm H2S with response and recovery time of 4 s and 46 s respectively. In contrast, the sensor fabricated with sputtered film shows a response of 30.6% at 1 ppm with response and recovery times of 19 s and 84 s respectively. This study clearly indicates that plasma oxidation is an efficient method for development of stable sensors.
A Suspended Low Power Gas Sensor With In-Plane Heater
(IEEE, 2017-02) Benedict, Samatha
An ultralow power suspended gas sensor with in-plane heater and nano gap sensor electrodes is presented. The heater and sensing electrodes, separated by 1-μm air gap, are processed using single lithography step with standard micro-fabrication techniques. Controlled electromigration is used to create a nanogap in the middle of the sensing electrode. The sol-gel grown ZnO is dispensed using a picoliter dispenser to bridge the nanogap electrode, created by electromigration, to get required metal oxide film as a sensing element. The gap between the electrode and heater is optimized by electrothermal simulation to obtain desired temperature profile on ZnO. The resulting device exhibits excellent sensing performance for hydrogen (~86% at 20 ppm) at 0.5 mW. A detailed characterization was carried out to analyze the performance of the device. This unique, in-plane structure is superior compared with the conventional out of plane structure in terms of the power efficiency and ease of processing.
An ultralow power nanosensor array for selective detection of air pollutants
(IOP, 2019-10) Benedict, Samatha
Semiconducting metal oxide gas sensors typically operate at a high temperature and consume hundreds of milliwatts of power. Therefore there is great demand for the development of a low-power gas-sensing technology that can sensitively and selectively detect the gas analytes present in the atmosphere. We report an ultralow-power nanosensor array platform, integrated with an independently controlled nanoheater of size 4 μm × 100 nm, which consumes ∼1.8 mW power when operated continuously at 300 °C. The heaters exhibit a fast thermal response time of less than 1 μs, and can be utilized to operate in duty cycle mode, leading to power saving. The active area of the nanosensor is 1 μm × 200 nm, defined by sensing electrodes with a nanogap of ∼200nm, leading to small form factor. As a proof of concept, each of the sensing elements in the array is functionalized with different sensing materials to demonstrate a low-power, sensitive and selective multiplexed gas-sensing technology for the simultaneous detection of CO (∼93.2% for 3 ppm at 300 °C), CO2 (∼76.3% for 1000 ppm at 265 °C), NO2 (∼2301% for 3 ppm at 150 °C) and SO2 (∼94% for 3 ppm at 265 °C). The technology described here uses scalable crossbar architecture for sensor elements, thus enabling the integration of additional sensing materials and making it customizable for specific applications.