Ibraheem Haneef

High Performance SOI-CMOS Wall Shear Stress Sensors

Here we present for the first time, a novel silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) MEMS thermal shear stress sensor for turbulent flow measurements based on aluminum hot-film as a sensing element. These devices have been fabricated using commercial 1 mum SOI-CMOS process followed by a deep reactive ion etch (DRIE) back-etch step, offering low cost and the option of circuit integration. The sensors have a good spatial resolution (size 130 mum times 130 mum) and a very efficient thermal isolation (due to their location on a 500 mum times 500 mum, low thermal conductivity silicon oxide membrane). Results show that these sensors have a high temperature coefficient of resistance (TCR) (0.319%/degC), a low power consumption (below 10 mW for 100degC temperature rise) and a high reproducibility within a wafer and from wafer to wafer. In constant temperature (CT) mode, the sensors exhibit an average sensitivity of 22 mV/Pa in a wall shear stress range of 0-1.5 Pa and an ultra-short time constant of only 17 mus, which corresponds to a high cut-off frequency of 39 kHz.

SOI diode temperature sensor operated at ultra high temperatures - a critical analysis

This paper investigates the performance of diode temperature sensors when operated at ultra high temperatures (above 250degC). A low leakage silicon on insulator (SOI) diode was designed and fabricated in a 1 mum CMOS process and suspended within a dielectric membrane for efficient thermal insulation. The diode can be used for accurate temperature monitoring in a variety of sensors such as microcalorimeters, IR detectors, or thermal flow sensors. A CMOS compatible micro-heater was integrated with the diode for local heating. It was found that the diode forward voltage exhibited a linear dependence on temperature as long as the reverse saturation current remained below the forward driving current. We have proven experimentally that the maximum temperature can be as high as 550degC. Long term continuous operation at high temperatures (400degC) showed good stability of the voltage drop. Furthermore, we carried out a detailed theoretical analysis to determine the maximum operating temperature and explain the presence of nonlinearity factors at ultra high temperatures.

Ultra-high temperature (≫ 300°C) suspended thermodiode in SOI CMOS technology

This paper reports for the first time on the performance and long term continuous operation of a suspended silicon on insulator (SOI) thermodiode with tungsten metallisation at temperatures beyond 300degC. The thermodiode has been designed and fabricated with minute saturation currents (due to both small size and the use of SOI technology) to allow an ultra-high temperature range and minimal nonlinearity. It was found that the thermodiode forward voltage drop vs temperature plot remains linear upto 500degC, with a non-linearity error of less than 7%. Extensive experimental results on performance of the thermodiode, fabricated using a CMOS (complimentary metal oxide semiconductor) SOI process have been presented. These results are backed up by infra red measurements and a range of 2D and 3D simulations using ANSYS and ISE software. The on-chip electronics for thermodiode and micro-heater drive, as well as the transducing circuit for the sensor were placed adjacent to the membrane. Moreover, we demonstrate that the thermodiode is considerably more reliable in long-term direct current operation at high temperatures when compared to the more classical resistive temperature detectors (RTDs) using CMOS metallisation layers (Tungsten or Aluminum). Finally, we believe that the thermodiode suffers less of piezojunction/piezo-resistive effects when compared to silicon based RTDs. For this we compare a membrane thermodiode with a reference thermodiode placed on the silicon substrate and assess their relative performance at elevated temperatures.

Use of nanocomposites to increase electrical “gain” in chemical sensors

We have investigated chemical sensors by combining silicon-on-insulator complementary-metal-oxide-semiconducting microtechnology with nanotechnology. The sensing materials were single-walled carbon nanotubes and poly(3,3‴-dialkyl-quarterthiophone). The devices containing only nanotubes or pure polymer provided minimal response, whereas the nanocomposite material (1wt.% of nanotubes in the polymer) provided excellent sensitivity/selectivity to the particular analyte monitored (hydrogen, ammonia, and acetone). We observed that even small amounts of gas doping (10ppb) resulted in exponential changes in the overall conductivity profile of the nanocomposite sensor, thus anticipating an element of “gain” within the chemical sensor.

Nanowire hydrogen gas sensor employing CMOS micro-hotplate

In this paper we present a novel hydrogen gas sensor comprising a high temperature SOI-MOS micro-hotplate and employing zinc oxide nanowires as the sensing material. The micro-hotplates were fabricated at a commercial SOI foundry followed by a backside deep reactive ion etch (DRIE) at a commercial MEMS foundry. Particular care was taken in designing the heater shape using a systematic parametric approach to achieve excellent temperature uniformity (within 1–2%) as shown by both simulations and experimental infra-red imaging results. Zinc oxide nanowires were grown on these devices and show promising responses to hydrogen with a response (Ra/Rh) of 50 at 100 ppm in argon. The devices possess a low D.C. power consumption of only 16 mW at 300°C and, being CMOS compatible, offer low unit cost in high volumes and full circuit integration. We believe that these devices have potential for application as a sub-

Minimizing the loss produced by a turbulent separation using vortex generator jets

1 hydrogen sensor with sub-1mW (pulsed mode) power consumption.

An SOI CMOS-Based Multi-Sensor MEMS Chip for Fluidic Applications.

Vortex generator jets have been applied to control a separating turbulent boundary layer on the suction surface of compressor blades in a linear cascade at high incidence. With the jets operating in a steady blowing mode, loss measurements were taken over a range of jet velocities. An increase in the jet blowing ratio yielded a reduction in the loss coefficient up to a blowing ratio of 70%. At this condition, a loss reduction of 61% was measured relative to the case with no control. Higher jet velocities yielded a slight increase in the loss coefficient. In order to explore the behavior of the boundary layer over this range of blowing ratios, four sets of experiments were performed: static pressure measurements, wall shear stress measurements, stereoscopic Particle Image Velocimetry (PIV) measurements and smoke flow visualization. The static pressure measurements showed that the point of separation moves downstream from 60% surface length with no control, to approximately 92% with a blowing ratio of 70%. At higher blowing ratios, the boundary layer remains attached up to the trailing edge. Shear stress measurements were taken on the suction surface using a streamwise array of novel, dual element MEMS hot-film sensors. The mean quasi-wall shear stress measured with the sensors indicated attached flow in the region of the jet holes and separated flow downstream at all blowing ratios including and below 50%. At a blowing ratio of 75%, the quasi-wall shear stress measurements suggest that the flow is attached, but close to separation. These results suggest that minimum loss is obtained at the blowing ratio required to just keep the boundary layer attached. This conclusion is approximate because the flow from the discrete jets is inherently three-dimensional, and so the separation location will vary across the span. The three-dimensionality of the flow produced by the jets was evident in the quasi-wall shear stress and PIV measurements, as well as the smoke flow visualization. A vortex skewed relative to the streamwise direction was identified in the PIV measurements. By correlating the location of this vortex with the shear stress measurements, this vortex was identified with a region of elevated shear stress. A second region of elevated shear stress was, however, identified between the vortices. Turbulent kinetic energy extracted from the PIV measurements allowed the identification of this region with secondary flow between the co-rotating vortices produced by adjacent jets.

Arrays of Parallel Connected Coaxial Multiwall-Carbon- Nanotube–Amorphous-Silicon Solar Cells

An SOI CMOS multi-sensor MEMS chip, which can simultaneously measure temperature, pressure and flow rate, has been reported. The multi-sensor chip has been designed keeping in view the requirements of researchers interested in experimental fluid dynamics. The chip contains ten thermodiodes (temperature sensors), a piezoresistive-type pressure sensor and nine hot film-based flow rate sensors fabricated within the oxide layer of the SOI wafers. The silicon dioxide layers with embedded sensors are relieved from the substrate as membranes with the help of a single DRIE step after chip fabrication from a commercial CMOS foundry. Very dense sensor packing per unit area of the chip has been enabled by using technologies/processes like SOI, CMOS and DRIE. Independent apparatuses were used for the characterization of each sensor. With a drive current of 10 µA–0.1 µA, the thermodiodes exhibited sensitivities of 1.41 mV/°C–1.79 mV/°C in the range 20–300 °C. The sensitivity of the pressure sensor was 0.0686 mV/(Vexcit kPa) with a non-linearity of 0.25% between 0 and 69 kPa above ambient pressure. Packaged in a micro-channel, the flow rate sensor has a linearized sensitivity of 17.3 mV/(L/min)−0.1 in the tested range of 0–4.7 L/min. The multi-sensor chip can be used for simultaneous measurement of fluid pressure, temperature and flow rate in fluidic experiments and aerospace/automotive/biomedical/process industries.