Smart chemical sensor application of ZnO nanowires grown on CMOS compatible SOI microheater platform

Smart chemical sensor based on CMOS(complementary metal-oxide- semiconductor) compatible SOI(silicon on insulator) microheater platform was realized by facilitating ZnO nanowires growth on the small membrane at the relatively low temperature. Our SOI microheater platform can be operated at the very low power consumption with novel metal oxide sensing materials, like ZnO or SnO2 nanostructured materials which demand relatively high sensing temperature. In addition, our sol-gel growth method of ZnO nanowires on the SOI membrane was found to be very effective compared with ink-jetting or CVD growth techniques. These combined techniques give us the possibility of smart chemical sensor technology easily merged into the conventional semiconductor IC application. The physical properties of ZnO nanowire network grown by the solution-based method and its chemical sensing property also were reported in this paper.

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 250°C). A low leakage Silicon On Insulator (SOI) diode was designed and fabricated in a 1 μm 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 550°C. Long term continuous operation at high temperatures (400°C) showed good stability of the voltage drop. Furthermore, we carried out a detailed theoretical analysis to determine the maximum operating temperature and exlain the presence of nonlinearity factors at ultra high temperatures. © 2008 IEEE.

Laminar to turbulent flow transition measurements using an array of SOI-CMOS MEMS wall shear stress sensors

The successful utilization of an array of silicon on insulator complementary metal oxide semiconductor (SOICMOS) micro thermal shear stress sensors for flow measurements at macro-scale is demonstrated. The sensors use CMOS aluminum metallization as the sensing material and are embedded in low thermal conductivity silicon oxide membranes. They have been fabricated using a commercial 1 μm SOI-CMOS process and a post-CMOS DRIE back etch. The sensors with two different sizes were evaluated. The small sensors (18.5 ×18.5 μm2 sensing area on 266 × 266 μm2 oxide membrane) have an ultra low power (100 °C temperature rise at 6mW) and a small time constant of only 5.46 μs which corresponds to a cut-off frequency of 122 kHz. The large sensors (130 × 130 μm2 sensing area on 500 × 500 μm2 membrane) have a time constant of 9.82 μs (cut-off frequency of 67.9 kHz). The sensors' performance has proven to be robust under transonic and supersonic flow conditions. Also, they have successfully identified laminar, separated, transitional and turbulent boundary layers in a low speed flow. © 2008 IEEE.

Improved infrared thermal imaging of a CMOS MEMS device

We report a technique which can be used to improve the accuracy of infrared (IR) surface temperature measurements made on MEMS (Micro-Electro-Mechanical- Systems) devices. The technique was used to thermally characterize a SOI (Silicon-On-Insulator) CMOS (Complementary Metal Oxide Semiconductor) MEMS thermal flow sensor. Conventional IR temperature measurements made on the sensor were shown to give significant surface temperature errors, due to the optical transparency of the SiO 2 membrane layers and low emissivity/high reflectivity of the metal. By making IR measurements on radiative carbon micro-particles placed in isothermal contact with the device, the accuracy of the surface temperature measurement was significantly improved. © 2010 EDA Publishing/THERMINIC.

Thermal characterization of SOI CMOS micro hot-plate gas sensors

This work reports on thermal characterization of SOI (silicon on insulator) CMOS (complementary metal oxide semiconductor) MEMS (micro electro mechanical system) gas sensors using a thermoreflectance (TR) thermography system. The sensors were fabricated in a CMOS foundry and the micro hot-plate structures were created by back-etching the CMOS processed wafers in a MEMS foundry using DRIE (deep reactive ion etch) process. The calibration and experimental details of the thermoreflectance based thermal imaging setup, used for these micro hot-plate gas sensor structures, are presented. Experimentally determined temperature of a micro hot-plate sensor, using TR thermography and built-in silicon resistive temperature sensor, is compared with that estimated using numerical simulations. The results confirm that TR based thermal imaging technique can be used to determine surface temperature of CMOS MEMS devices with a high accuracy. © 2010 EDA Publishing/THERMINIC.

RNAi, DRD1, and histone methylation actively target developmentally important Non-CG DNA methylation in Arabidopsis

Cytosine DNA methylation protects eukaryotic genomes by silencing transposons and harmful DNAs, but also regulates gene expression during normal development. Loss of CG methylation in the Arabidopsis thaliana met1 and ddm1 mutants causes varied and stochastic developmental defects that are often inherited independently of the original met1 or ddm1 mutation. Loss of non-CG methylation in plants with combined mutations in the DRM and CMT3 genes also causes a suite of developmental defects. We show here that the pleiotropic developmental defects of drm1 drm2 cmt3 triple mutant plants are fully recessive, and unlike phenotypes caused by met1 and ddm1, are not inherited independently of the drm and cmt3 mutations. Developmental phenotypes are also reversed when drm1 drm2 cmt3 plants are transformed with DRM2 or CMT3, implying that non-CG DNA methylation is efficiently re-established by sequence-specific signals. We provide evidence that these signals include RNA silencing though the 24-nucleotide short interfering RNA (siRNA) pathway as well as histone H3K9 methylation, both of which converge on the putative chromatin-remodeling protein DRD1. These signals act in at least three partially intersecting pathways that control the locus-specific patterning of non-CG methylation by the DRM2 and CMT3 methyltransferases. Our results suggest that non-CG DNA methylation that is inherited via a network of persistent targeting signals has been co-opted to regulate developmentally important genes. © 2006 Chan et al.

A high temperature SOI CMOS NO2 sensor

For more than 20 years researchers have been interested in developing micro-gas sensors based on silicon technology. Most of the reported devices are based on micro-hotplates, however they use materials that are not CMOS compatible, and therefore are not suitable for large volume manufacturing. Furthermore, they do not allow the circuitry to be integrated on to the chip. CMOS compatible devices have been previously reported. However, these use polysilicon as the heater material, which has long term stability problems at high temperatures. Here we present low power, low cost SOI CMOS NO2 sensors, based on high stability single crystal silicon P+ micro-heaters platforms, capable of measuring gas concentrations down to 0.1 ppm. We have integrated a thin tungsten molybdenum oxide layer as a sensing material with a foundry-standard SOI CMOS micro-hotplate and tested this to NO2. We believe these devices have the potential for use as robust, very low power consumption, low cost gas sensors. © 2011 American Institute of Physics.

High temperature robust SOI ethanol sensor

In this paper we present a robust SOI-CMOS ethanol sensor based on a tungsten-doped lanthanum iron oxide sensing material. The device shows response to gas, has low power consumption, good uniformity, high temperature stability and can be manufactured at low cost and with integrated circuitry. The platform is a tungsten-based CMOS micro-hotplate that has been shown to be stable for over two thousand hours at a high temperature (600°C) in a form of accelerated life test. The tungsten-doped lanthanum iron oxide was deposited on the micro-hotplate as a slurry with terpineol using a syringe, dried and annealed. Preliminary gas testing was done and the material shows response to ethanol vapour. These results are promising and we believe that this combination of a robust CMOS micro-hotplate and a good sensing material can form the basis for a commercial CMOS gas sensor. © 2011 Published by Elsevier Ltd.

UK-NEES - Distributed hybrid testing between Bristol, Cambridge and Oxford Universities: Connecting structural dynamics labs to a geotechnical centrifuge

Distributed hybrid testing is a natural extension to and builds upon the local hybrid testing technique. Taking advantage of the hybrid nature of the test, it allows a sharing of resources and expertise between researchers from different disciplines by connecting multiple geographically distributed sites for joint testing. As part of the UK-NEES project, a successful series of three-site distributed hybrid tests have been carried out between Bristol, Cambridge and Oxford Universities. The first known multi-site distributed hybrid tests in the UK, they connected via a dedicated fibre network, using custom software, the geotechnical centrifuge at Cambridge to structural components at Bristol and Oxford. These experiments were to prove the connection and useful insights were gained into the issues involved with this distributed environment. A wider aim is towards providing a flexible testing framework to facilitate multi-disciplinary experiments such as the accurate investigation of the influence of foundations on structural systems under seismic and other loading. Time scaling incompatibilities mean true seismic soil structure interaction using a centrifuge at g is not possible, though it is clear that distributed centrifuge testing can be valuable in other problems. Development is continuing to overcome the issues encountered, in order to improve future distributed tests in the UK and beyond.

SOI membrane-based pressure sensor in stress sensitive differential amplifier configuration

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar). © 2012 IEEE.