Smart sensors

This paper is a state-of-the-art review of solid-state integrated and smart sensors. Smart sensors are defined as sensors that provide analog signal processing of signals recorded by sensors, digital representation of the analog signal, address and data transfer through a bidirectional digital bus and manipulation and computation of the sensor-derived data. In this paper the overall architecture and functions of circuit blocks necessary for smart sensors are presented and discussed. Circuit fabrication technologies are briefly discussed and CMOS technology is found to be ideally suited for many sensor applications. The challenges and techniques for the packaging of smart sensors are briefly reviewed and several specific examples of solid-state integrated and smart sensors are presented. It is believed that smart sensors will be needed in future closed-loop instrumentation and that control systems will be required in many application areas, including automative, health care, industrial processing and consumer electronics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49022/2/jm910202.pd

Measurement of fracture stress, young's modulus, and intrinsic stress of heavily boron-doped silicon microstructures

Heavily boron-doped silicon microstructures fabricated using deep-boron diffusions and boron etch-stops have been widely used in a variety of integrated sensors and actuators. For many applications, having knowledge of the mechanical properties such as Young's modulus, intrinsic stress, and fracture stress of these films is very important in predicting the response parameters of the sensors and actuators that utilize them. These parameters include mechanical resonant frequency, sensitivity, bandwidth, linearity, and operating range. This paper describes the measurement of fracture stress, Young's modulus, and intrinsic stress of boron-doped silicon microstructures at doping concentrations above 5 x 1019 cm-3. The measurement of fracture stress is performed using 15 microm thick cantilever beams of widths ranging from 20 to 150 microm. The beams were bent to fracture and the maximum fracture stress was measured to be [approximate] 1.8 x 1010 dyne cm-2 which is a factor of about six higher than silicon structures with larger dimensions (bulk silicon). Young's modulus and intrinsic stress were measured using a novel custom-designed doubly supported beam (bridge) structure. The measurement technique uses the characteristic pull-in voltage of the beam as electrostatic voltage is applied across an air gap capacitor in the middle of the beam, which causes the bridge to collapse. The Young's modulus for (110)-oriented silicon was measured to be [approximate] (2-2.2) x 1012 dyne cm-2 which is 20%-30% higher than undoped silicon. The measured intrinsic stress of 1.83 x 108 dyne cm-2 agrees well with the measured pressure-deflection characteristics of thin diaphragms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27640/1/0000016.pd

Criticality of natural absorbing states

We study a recently introduced ladder model which undergoes a transition between an active and an infinitely degenerate absorbing phase. In some cases the critical behaviour of the model is the same as that of the branching annihilating random walk with $N\geq 2$ species both with and without hard-core interaction. We show that certain static characteristics of the so-called natural absorbing states develop power law singularities which signal the approach of the critical point. These results are also explained using random walk arguments. In addition to that we show that when dynamics of our model is considered as a minimum finding procedure, it has the best efficiency very close to the critical point.Comment: 6 page

A generic micromachined silicon platform for high-performance RF passive components

This paper describes the development of a micromachined silicon platform fabricated using the dissolved wafer process that supports: (1) high self-resonance frequency and quality factor inductors suspended on a dielectric membrane, (2) low-loss thin-film capacitors, and (3) polysilicon resistors. The process uses deep boron diffusion to create silicon anchors, which support a stress compensated dielectric membrane. A thick resist mold is used to gold electroplate the inductor, top capacitor plate, and bonding pads. This platform can be used to build miniature high-performance transceivers or other RF subsystems using either hybrid-attached surface-mount components or flip-chip bonded RF circuits. Using this technique, a Colpitts transmitter with a five-turn dielectric suspended inductor was designed and fabricated. The transmitter oscillates in the frequency band of 275-375 MHz, consumes 200 µA when operated continuously and 100 µA when amplitude modulated (on-off keying) at a rate of 1 Mbps (50% duty cycle).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49026/2/jm0310.pd

Batch-assembled multi-level micromachined mechanisms from bulk silicon

The authors report on the development of a new technology intended for the wafer level fabrication and assembly of fully integrated micromechanisms. The technology is based on a boron-doped bulk silicon dissolved wafer process that has been used to fabricate a variety of micromechanical devices. The overall process utilizes three wafers: two silicon and one glass. All the major mechanical elements, including gears and micromotors, are fabricated from one silicon wafer, whereas the mechanical links between these elements are fabricated from a second silicon wafer. These wafers are successively aligned and bonded to a glass wafer which forms the substrate and are then dissolved in EDP to free the mechanisms. This procedure permits wafer-level batch assembly of micromechanical systems. A number of bulk silicon electrostatic micromotors 5-10 mu m thick and gear trains have been fabricated and linked to each other on the same chip.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49023/2/jm920203.pd

A CMOS-compatible high aspect ratio silicon-on-glass in-plane micro-accelerometer

This paper presents a post-CMOS-compatible micro-machined silicon-on-glass (SOG) in-plane capacitive accelerometer. The accelerometer is a high aspect ratio structure with a 120 µm thick single-crystal silicon proof-mass and 3.4 µm sense gap, bonded to a glass substrate. It is fabricated using a simple 3-mask, 5-step process, and is fully CMOS compatible. A CMOS switched-capacitor readout circuit and an oversampled Σ–delta modulator are used to read out capacitance changes from the accelerometer. The CMOS chip is 2.6 × 2.4 mm2 in size, utilizes chopper stabilization and correlated double sampling techniques, has a 106 dB open-loop dynamic range, a low input offset of 370 µV, and can resolve better than 20 aF. The accelerometer system has a measured sensitivity of 40 mV g−1 and input referred noise density of 79 µg Hz−1/2. Using the SOG configuration, a post-CMOS monolithic integration technique is developed. The integration technique utilizes dielectric bridges, silicon islands and the SOG configuration to obtain a simple, robust and post-CMOS-compatible process. Utilizing this technique, an integrated SOG accelerometer has been fabricated using the University of Michigan 3 µm CMOS process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49037/2/jmm5_2_013.pd

A wide-range micromachined threshold accelerometer array and interface circuit

This paper presents a complete threshold acceleration detection microsystem comprising an array of threshold accelerometers and a low power interface circuit. The sensors were designed and fabricated using the bulk-silicon dissolved-wafer process. The process offers a wide latitude in sensor threshold levels, as demonstrated in the fabrication of devices with levels of 1.5-1000 g, bandwidths of 45 Hz to 40 kHz, with mass sizes ranging from 0.015 µg to 0.7 µg, and low-resistance gold-gold contacts for the switch. The interface circuit dissipates less than 300 µW, measures 2.2 mm×2.2 mm; it was fabricated in-house using a standard 3 µm, p-well CMOS (complementary metal oxide semiconductor) process, and is connected to the sensor chip in a multi-chip module. The key aspects of the microsystem are the implementation of sensor redundancy and supporting circuit logic to improve detection accuracy and fault tolerance, which are crucial factors in many applications. In addition, the microsystem supports communication with a standard microcontroller bus in a smart sensor network.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49029/2/jm1206.pd

Sero-prevalence of helicobacter pylori infection in Neyshabur, Iran, during 2010-2015

Backgrounds & Objective: The Helicobacter pylori prevalence has continuously decreased during recent years in Iran. The current study aimed at determining H. pylori prevalence in Neyshabur city, Northeast Iran, during 2010-2015. Methods: The current epidemiologic survey was conducted in Neyshabur from 2010 to 2015 to determine the prevalence of H. pylori infection. A total of 11596 participants (3681 male with the mean age of 31.7±6.2 years and 7915 female with mean age of 68.3±4.7 years) were included. The enzyme-linked immunosorbent assay kits for the detection of H. pylori and Stat Fax 3200® Microplate Reader (USA) with a sensitivity of 95% and specificity of 98% were used. Titers above 12 units were considered positive for IgG, IgA, and IgM (negative 12 U). The Chi-square t test and F test were used to analyze data. Results: The overall IgA, IgG, and IgM seropositive samples among the study participants were 852 (7.2%), 9000 (72.8%), and 1256 (5.2%), respectively. The IgA seropositivity was significantly high among the age group above 51 years, compared with the other age groups. Moreover, the IgG and IgM seropositivity were significantly high among the age groups 41 to 50 and 31 to 40 years respectively, compared with the other age groups. There was no significant difference between male and female cases regarding IgA and IgG seropositive samples, but IgM level was significantly higher among females, compared with that of the male cases. Furthermore, there was no significant alteration in IgA, IgG, and IgM seropositivity during 2010-2014 in Neyshabur. Conclusion: The prevalence of H. pylori in Neyshabur was high in the healthy population. Furthermore, the H. pylori prevalence did not change from 2010 to 2014 in the studied city. Effective approaches to improve health, educational, and socioeconomic status should be implemented to minimize and control H. pylori infection