Sazia A. Eliza

Flexible capacitive sensors for high resolution pressure measurement

Thin, flexible, robust capacitive pressure sensors have been the subject of research in many fields where axial strain sensing with high spatial resolution and pressure resolution is desirable for small loads, such as tactile robotics and biomechanics. Simple capacitive pressure sensors have been designed and implemented on flexible substrates in general agreement with performance predicted by an analytical model. Two designs are demonstrated for comparison. The first design uses standard flex circuit technology, and the second design uses photolithography techniques to fabricate capacitive sensors with higher spatial and higher pressure resolution. Sensor arrays of varying sensor size and spacing are tested with applied loads from 0 to 1 MPa. Pressure resolution and linearity of the sensors are significantly improved with the miniaturized, custom fabricated sensor array compared to standard flexible circuit technology.

A low-power capacitance measurement circuit with high resolution and high degree of linearity

This paper has presented a low-power capacitance read-out circuit which could be used for biomedical sensor applications. The differential structure of the system eliminates even order distortion. The entire system manifests two current sense amplifiers, two diode rectifiers and one instrumentation amplifier. The circuit has been realized using TSMC 0.35 mum bulk CMOS process. The circuit operates with a 3 V power supply and consumes 5.384 mW of power. Simulation results show that the circuit has a sensitivity of 1.32 mV for 1 fF capacitance change. Measurement results for different capacitance variations demonstrate a change of 10.8 mV for 8.8 fF variation.

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.

Integration of a dose control circuit with a vertically aligned nanofiber field emission device

This paper discusses the complete integration of the prototype digital electrostatic focused e-beam array direct-write lithography (DEAL) device with the dose control circuitry (DCC). The DCC regulates charge emission from the vertically aligned carbon nanofibers (VACNFs) and prevents resists from being over exposed during the e-beam lithography process. The emission of electrons from the VACNF tip requires relatively high voltage. The I-V characteristic of a typical VACNF based device is presented with threshold voltage of ~75 V. The DCC built using a standard 5 V digital CMOS process cannot handle such voltage levels

Ultra-high sensitivity gas sensors based on GaN HEMT structures

This paper presents simulation of GaN high electron mobility transistor (HEMT) based device structures for the detection of toxic and hazardous gases like carbon monooxide (CO) and hydrogen (H2), respectively. AlGaN/GaN heterostructures show large potential as sensors due to the presence of 2-dimensional electron gas (2-DEG) at the heterointerface. Due to widebandgap material properties, GaN based devices are highly suitable for extreme-environment applications. The sensors are proposed selective towards specific targets by the two different gate structures. The simulated AlGaN/GaN based HEMT with Pt/AlGaN Schottky gate structure can detect hydrogen gas with the concentrations as low as ppb level and with the linear output variations from ∼ ppb to 100 ppm level. A new gate structure based on nanocrystalline stannic oxide (α-SnO2) layer for the selective and sensitive detection of CO gas is proposed. We report that the AlGaN/GaN HEMT structure with Pt/α-SnO2/AlGaN Metal-Oxide-Semiconductor (MOS) gate can be used to detect sub-ppm level of CO with the linear response upto 500 ppm.

Analysis of AlGaN/GaN HEMT modulated by photosystem I reaction centers

This paper presents for the first time a practical substitute to the laboratory (KFM) techniques for electrical characterization of PS I reaction centers which is necessary precondition to eventual commercial realization of molecular photovoltaic devices. The experimental study and an analytical model have been presented to investigate the charge effects of PS I reaction centers on the characteristics of AlGaN/GaN high electron mobility transistor (HEMT).

A Precision Dose Control Circuit for Maskless E-Beam Lithography With Massively Parallel Vertically Aligned Carbon Nanofibers

This paper describes a highly accurate dose control circuit (DCC) for the emission of a desired number of electrons from vertically aligned carbon nanofibers (VACNFs) in a massively parallel maskless e-beam lithography system. The parasitic components within the VACNF device cause a premature termination of the electron emission, resulting in underexposure of the photoresist. In this paper, we compensate for the effects of the parasitic components and noise while reducing the area of the chip and achieving a precise count of emitted electrons from the VACNFs to obtain the optimum dose for the e-beam lithography.

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.

A precision dose control circuit for vertically aligned carbon nanofiber based maskless lithography

This paper presents a precision control circuit for the emission of desired number of electrons from vertically aligned carbon nanofibers (VACNFs) for the realization of a massively parallel maskless e-beam lithography system. The digitally addressable field emission arrays (DAFEAs) of the VACNFs function as the lithography heads for massively parallel e-beam exposure of resist eliminating the cost of photomasks [1]. A dose control circuit (DCC) to prevent under- or over-exposure of the resist has been integrated [2] by our research group. This paper describes further improvements in dose control electronics to reduce the parasitic effects while reducing the area of the chip and lowering the count of electrons for achieving the optimum dose from each of the nanofiber emitters.