Salwa Mostafa

Low-Power Low-Voltage Current Readout Circuit for Inductively Powered Implant System

Low voltage and low power are two key requirements for on-chip realization of wireless power and data telemetry for applications in biomedical sensor instrumentation. Batteryless operation and wireless telemetry facilitate robust, reliable, and longer lifetime of the implant unit. As an ongoing research work, this paper demonstrates a low-power low-voltage sensor readout circuit which could be easily powered up with an inductive link. This paper presents two versions of readout circuits that have been designed and fabricated in bulk complementary metal-oxide semiconductor (CMOS) processes. Either version can detect a sensor current in the range of 0.2 μA to 2 μA and generate square-wave data signal whose frequency is proportional to the sensor current. The first version of the circuit is fabricated in a 0.35-μ m CMOS process and it can generate an amplitude-shift-keying (ASK) signal while consuming 400 μ W of power with a 1.5-V power supply. Measurement results indicate that the ASK chip generates 76 Hz to 500 Hz frequency of a square-wave data signal for the specified sensor current range. The second version of the readout circuit is fabricated in a 0.5-μ m CMOS process and produces a frequency-shift-keying (FSK) signal while consuming 1.675 mW of power with a 2.5-V power supply. The generated data frequency from the FSK chip is 1 kHz and 9 kHz for the lowest and the highest sensor currents, respectively. Measurement results confirm the functionalities of both prototype schemes. The prototype circuit has potential applications in the monitoring of blood glucose level, lactate in the bloodstream, and pH or oxygen in a physiological system/environment.

Development of MEMS based pyroelectric thermal energy harvesters

The efficient conversion of waste thermal energy into electrical energy is of considerable interest due to the huge sources of low-grade thermal energy available in technologically advanced societies. Our group at the Oak Ridge National Laboratory (ORNL) is developing a new type of high efficiency thermal waste heat energy converter that can be used to actively cool electronic devices, concentrated photovoltaic solar cells, computers and large waste heat producing systems, while generating electricity that can be used to power remote monitoring sensor systems, or recycled to provide electrical power. The energy harvester is a temperature cycled pyroelectric thermal-to-electrical energy harvester that can be used to generate electrical energy from thermal waste streams with temperature gradients of only a few degrees. The approach uses a resonantly driven pyroelectric capacitive bimorph cantilever structure that potentially has energy conversion efficiencies several times those of any previously demonstrated pyroelectric or thermoelectric thermal energy harvesters. The goals of this effort are to demonstrate the feasibility of fabricating high conversion efficiency MEMS based pyroelectric energy converters that can be fabricated into scalable arrays using well known microscale fabrication techniques and materials. These fabrication efforts are supported by detailed modeling studies of the pyroelectric energy converter structures to demonstrate the energy conversion efficiencies and electrical energy generation capabilities of these energy converters. This paper reports on the modeling, fabrication and testing of test structures and single element devices that demonstrate the potential of this technology for the development of high efficiency thermal-to-electrical energy harvesters.

Review of pyroelectric thermal energy harvesting and new MEMs based resonant energy conversion techniques

Harvesting electrical energy from thermal energy sources using pyroelectric conversion techniques has been under investigation for over 50 years, but it has not received the attention that thermoelectric energy harvesting techniques have during this time period. This lack of interest stems from early studies which found that the energy conversion efficiencies achievable using pyroelectric materials were several times less than those potentially achievable with thermoelectrics. More recent modeling and experimental studies have shown that pyroelectric techniques can be cost competitive with thermoelectrics and, using new temperature cycling techniques, has the potential to be several times as efficient as thermoelectrics under comparable operating conditions. This paper will review the recent history in this field and describe the techniques that are being developed to increase the opportunities for pyroelectric energy harvesting. The development of a new thermal energy harvester concept, based on temperature cycled pyroelectric thermal-to-electrical energy conversion, are also outlined. The approach uses a resonantly driven, pyroelectric capacitive bimorph cantilever structure that can be used to rapidly cycle the temperature in the energy harvester. The device has been modeled using a finite element multi-physics based method, where the effect of the structure material properties and system parameters on the frequency and magnitude of temperature cycling, and the efficiency of energy recycling using the proposed structure, have been modeled. Results show that thermal contact conductance and heat source temperature differences play key roles in dominating the cantilever resonant frequency and efficiency of the energy conversion technique. This paper outlines the modeling, fabrication and testing of cantilever and pyroelectric structures and single element devices that demonstrate the potential of this technology for the development of high efficiency thermal-toelectrical energy conversion devices.

Integrated MOSFET-Embedded-Cantilever-Based Biosensor Characteristic for Detection of Anthrax Simulant

In this work, MOSFET-embedded cantilevers are configured as microbial sensors for detection of anthrax simulants, Bacillus thuringiensis. Anthrax simulants attached to the chemically treated gold-coated cantilever cause changes in the MOSFET drain current due to the bending of the cantilever which indicates the detection of anthrax simulant. Electrical properties of the anthrax simulant are also responsible for the change in the drain current. The test results suggest a detection range of 10 μL of stimulant test solution (a suspension population of 1.3 × 107 colony-forming units/mL diluted in 40% ethanol and 60% deionized water) with a linear response of 31 μA/μL.

A low-power sensor read-out circuit with FSK telemetry for inductively-powered implant system

This paper presents a low-power sensor read-out circuit with FSK telemetry option. The proposed system consists of a data generator block and a FSK generator block. The data generator block converts a sensor current to a square wave data signal whereas the FSK generator block produces two different frequencies depending upon the value of the data signal. The relatively simple architecture of the proposed system facilitates the low-voltage and low-power operation. The system has been designed using AMI 0.5 mum CMOS process. Simulation results show that the proposed system can detect a sensor current in the range of 50 nA to 5 muA and the total power consumption is 431 muW with a 3.3 V supply. The circuit is ready to be submitted for monolithic integration.

Microcantilever Array Pressure Measurement System for Biomedical Instrumentation

An analog signal processing integrated circuit for microcantilever array has been designed for pressure measurement in biomedical applications. The chip consists of analog multiplexer, instrumentation amplifier, sample-and-hold circuit, on-chip voltage and current references, successive approximation register analog-to-digital converter (ADC) and digital control unit. Root sum square (RSS) error from the overall pressure measurement system including microcantilever array and the application specific integrated circuit (ASIC) is only ±1.79 KPa within the measurement range of 0-300 KPa. The 8-bit ADC attains 45.4 dB signal-to-noise-and-distortion ratio (SNDR) and 56.4 dB spurious-free dynamic range (SFDR), while operating at 772 KHz. The integrated circuit has been fabricated using 0.35-¿m 2-poly 4-metal CMOS process technology. The chip occupies an area of 1.54 mm2 and consumes 17.8 mW of power with a single 3.3 V supply.

A digitally controllable current readout circuit and modulator unit for remote monitoring and biotelemetry applications

Healthcare providers are depending on remote patient monitoring system more and more to treat a patient before the conditions become acute. Low-power electronics is an integral part of the remote patient monitoring system which is required for data acquisition, signal processing and data transmission. This work reports a low-power digitally controllable current readout circuit and a modulator unit designed for remote patient monitoring system. The current readout block converts current (0.2 µA to 5 µA) from biosensors to a data signal whose frequency is proportional to the sensor current. A switched capacitor based modulator is realized which modulates the data using a low-power digital modulation scheme. The current readout and the modulator units are digitally controllable to save power and to provide either ASK or FSK modulated output signal. The circuit is simulated using a 0.35-µm standard CMOS process and it occupies less than 0.053 mm2 of chip area. Power consumption of the circuit varies from 44 µW to 57 µW for 0.2 µA to 5 µA input current with 1.5 V supply, which is very attractive for biosensor applications.

Label free detection of human MIG using AlGaN/GaN high electron mobility transistor

The paper demonstrates a novel way of detecting Monokine induced by interferon gamma (MIG) in physiological condition (150mM phosphate buffer solution) using a two terminal device. To provide specific MIG detection capability, anti-MIG IgG molecular affinity interface receptors were formed on a short self-assembled monolayer (SAM) on a floating gold sensing gate of a biochemically modified AlGaN/GaN high electron mobility transistor (HEMT) device. Floating gate configuration used for biomolecule detection eliminates the need of external gate voltage and represents purely the effect of biomolecules immobilization and binding events on the gate surface.

GaN-AlGaN high electron mobility transistors for multiple biomolecule detection such as photosystem I and human MIG

This paper demonstrates a novel way of using a single type of high electron mobility transistor (HEMT) device for detecting two kinds of biomolecules (Photosystem I and recombinant human monokine induced by interferon gamma, MIG). MIG was successfully detected in 150 mM concentration of phosphate buffer solution (PBS). Floating gate configuration used for biomolecule detection eliminates the need of external gate voltage and represents purely the effect of biomolecules immobilization and binding events on the gate surface.

Modeling of AlGaN/GaN HEMT based stress sensors

GaN based devices show great potential for high power, high frequency and extreme-environment applications. Due to spontaneous and piezoelectric polarization properties, these devices are also suitable for pressure monitoring or detection of biomolecules causing surface stress. Therefore, GaN based monolithic sensor system can be applied for the detection of biomolecules or pressure imaging for biomedical applications, sensor data processing and transmission of the sensor data even in extreme environmental conditions. This paper investigates the analytical performance of GaN high electron mobility transistor (HEMT) device for the induced strain due to external pressure and surface stress. Analytical expressions for the conductance-stress behavior of the sensor have been developed. The change in two-dimensional electron gas density at the heterointerface of AlGaN/GaN layers resulting from the change in polarizations causes change in the output current of the device. The effects of both the tensile and the compressive strains due to the external force have been studied. This model can be effectively applied to the measurement of target force and to the detection of polar or nonpolar biomolecules.