Integrated sensors in biological environments

This paper reviews the application and operation of integrated sensors and actuators in biological and physiological environments. Integrated transducers are widely employed for invasive and non-invasive patient monitoring, for recording and understanding biological events and systems, for delivery of chemicals and electrical stimuli into the body, and as a means for eventual realization of closed-loop visual, auditory and muscular prostheses. The state-of-the-art in the development of precision microstructures, interface electronics and signal processing, and packaging and encapsulation for integrated transducers operating in biological environments are discussed. The technologies derived from research on biomedical integrated sensors that have been applied to sensors used in other application areas are presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28889/1/0000725.pd

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

Harvesting traffic-induced vibrations for structural health monitoring of bridges

This paper discusses the development and testing of a renewable energy source for powering wireless sensors used to monitor the structural health of bridges. Traditional power cables or battery replacement are excessively expensive or infeasible in this type of application. An inertial power generator has been developed that can harvest traffic-induced bridge vibrations. Vibrations on bridges have very low acceleration (0.1–0.5 m s _2 ), low frequency (2–30 Hz), and they are non-periodic. A novel parametric frequency-increased generator (PFIG) is developed to address these challenges. The fabricated device can generate a peak power of 57 µW and an average power of 2.3 µW from an input acceleration of 0.54 m s _2 at only 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration (0.54–9.8 m s _2 ) and frequency range (up to 30 Hz) without any modifications or tuning. Its performance was tested along the length of a suspension bridge and it generated 0.5–0.75 µW of average power without manipulation during installation or tuning at each bridge location. A preliminary power conversion system has also been developed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90794/1/0960-1317_21_10_104005.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