Tri-axis convective accelerometer with closed-loop heat source

In this paper, we report the details and findings of a study on tri-axis convective accelerometer, which is designed with the closed-loop type heat source and thermal sensing hotwire elements. The closed-loopheat source enhances the convective flow to the central part where a hotwire is placed to measure the vertical component of acceleration. The simulation was conducted using numerical analysis, and the devicewas prototyped by additive manufacturing. The device, functioning as a tilt sensor and an accelerometer,was tested up to acceleration of 20 g. The experiments were successfully conducted and the experimental results agreed reasonably with those obtained by numerical analysis. The results demonstrated that the closed-loop heat source could reduce the cross effect between the acceleration components. The scalefactor and cross-sensitivity had the values of 0.26 micro�V/g and 1.2%, respectively. The cross-sensitivity andthe effects of heating power were also investigated in this study

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

A microchip optomechanical accelerometer

The monitoring of accelerations is essential for a variety of applications ranging from inertial navigation to consumer electronics. The basic operation principle of an accelerometer is to measure the displacement of a flexibly mounted test mass; sensitive displacement measurement can be realized using capacitive, piezo-electric, tunnel-current, or optical methods. While optical readout provides superior displacement resolution and resilience to electromagnetic interference, current optical accelerometers either do not allow for chip-scale integration or require bulky test masses. Here we demonstrate an optomechanical accelerometer that employs ultra-sensitive all-optical displacement read-out using a planar photonic crystal cavity monolithically integrated with a nano-tethered test mass of high mechanical Q-factor. This device architecture allows for full on-chip integration and achieves a broadband acceleration resolution of 10 \mu g/rt-Hz, a bandwidth greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical power requirements. Moreover, the nano-gram test masses used here allow for optomechanical back-action in the form of cooling or the optical spring effect, setting the stage for a new class of motional sensors.Comment: 16 pages, 9 figure

Design and micro-fabrication of tantalum silicide cantilever beam threshold accelerometer

Microfabricated threshold accelerometers were successfully designed and fabricated following a careful analysis of the electrical, mechanical, and fabrication issues inherent to micron-sized accelerometers. A uniform cantilever beam was chosen because of the simplicity of design and fabrication. New models for the electrostatic force exerted on the cantilever beam were developed and calculations were made that accurately predicted the electrical characteristics of the accelerometer. The calculations also provided design guidelines for optimizing the accelerometer dimensions. Computer simulation demonstrated that the error of the electrostatic force, calculated using the most accurate model, was within 2% of the actual force which was obtained by integrating the closed formula, through the bent beam curvature, for device parameters designed to detect an acceleration of 50 g. Conversely, it was shown that the widely used conventional parallel plate model had an error of approximately 90%. Novel surface micromachining process steps were successfully developed to fabricate the cantilever beam accelerometers. Sputter deposited tantalum silicide and commercially available spin-on-glass were used as a structural layer and a sacrificial layer, respectively. The dependence of resistivity, crystalline structure, Young\u27s modulus, and hardness of the tantalum silicide films on the annealing temperatures were measured. These results were employed to design accelerometers that were successfully operated. Excluding the metallization steps, only two masks and four photolithography steps were required. However, both positive and negative photoresists had to be utilized. NJIT\u27s standard photolithography steps were used for positive photoresist; however for the negative photoresist a specially developed multi-puddle process was used to obtain 4 micron resolution. Electrostatic attraction tests, of accelerometers, were performed using the Keithley current-voltage measurement system. These tests used deflection voltages ranging from 2.2 to 37.0 volts, corresponding to threshold acceleration levels from 580 to 18,500 g. Nearly 70 percent of the threshold voltage results fell within the expected error limits set by the accuracy of the device dimensions when processing tolerances were taken into account including the thickness variation caused by 8% uncertainty in the buffered HF etch rate of tantalum silicide. Some accelerometers were closed and opened 3 times without failure. The accelerometers tended to break after 3 times of operation and this was attributed to the welding of contacts. Centrifuge acceleration tests of accelerometers were carried out in a specially designed centrifuge in an acceleration range of 282 to 11,200 g. Nearly 80 percent of the threshold acceleration results fell within the expected error limits set by the accuracy of the device dimensions when processing tolerances were taken into account

Micromachined Artificial Haircell

A micromachined artificial sensor comprises a support coupled to and movable with respect to a substrate. A polymer, high-aspect ratio cilia-like structure is disposed on and extends out-of-plane from the support. A strain detector is disposed with respect to the support to detect movement of the support

Fundamental concepts of integrated and fiber optic sensors

This chapter discusses fiber optic and integrated optic sensor concepts. Unfortunately, there is no standard method to categorize these sensor concepts. Here, fiber optic and integrated optic sensor concepts will be categorized by the primary modulation technique. These modulation techniques have been classified as: intensity, phase, wavelength, polarization, and time/frequency modulation. All modulate the output light with respect to changes in the physical or chemical property to be measured. Each primary modulation technique is then divided into fiber optic and integrated optic sections which are treated independently. For each sensor concept, possible sensor applications are discussed. The sensors and references discussed are not exhaustive, but sufficient to give the reader an overview of sensor concepts developed to date. Sensor multiplexing techniques such as wavelength division, time division, and frequency division will not be discussed as they are beyond the scope of this report

Development and Packaging of Microsystems Using Foundry Services

Micro-electro-mechanical systems (MEMS) are a new and rapidly growing field of research. Several advances to the MEMS state of the art were achieved through design and characterization of novel devices. Empirical and theoretical model of polysilicon thermal actuators were developed to understand their behavior. The most extensive investigation of the Multi-User MEMS Processes (MUMPs) polysilicon resistivity was also performed. The first published value for the thermal coefficient of resistivity (TCR) of the MUMPs Poly 1 layer was determined as 1.25 x 10(exp -3)/K. The sheet resistance of the MUMPs polysilicon layers was found to be dependent on linewidth due to presence or absence of lateral phosphorus diffusion. The functional integration of MEMS with CMOS was demonstrated through the design of automated positioning and assembly systems, and a new power averaging scheme was devised. Packaging of MEMS using foundry multichip modules (MCMs) was shown to be a feasible approach to physical integration of MEMS with microelectronics. MEMS test die were packaged using Micro Module Systems MCM-D and General Electric High Density Intercounect and Chip-on-Flex MCM foundries. Xenon difluoride (XeF2) was found to be an excellent post-packaging etchant for bulk micromachined MEMS. For surface micromachining, hydrofluoric acid (HF) can be used

DEVELOPMENT OF MEMS THERMOPILES AND RELATED APPLICATIONS

Ph.DDOCTOR OF PHILOSOPH