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A silicon piezoresistive stress sensor is developed to measure the three components of the orthodontic forces of a tooth in invisible aligners. The stress sensor chip consists of multiple piezoresistor rosettes, and is fixed on the tooth surface to measure the orthodontic force induced stresses. An inverse problem algorithm is established to reconstruct the orthodontic forces of the tooth from the measured stresses. A key thinning process is developed using chemical-mechanical polishing to thin the sensor chip from 650 to 100 , such that it can be accommodated to the limited space between the aligner and the tooth, without much influence on the orthodontic force. The ultra-thin thickness enables the sensor chip to be compliance with tooth deformation, and improves the stress measurement sensitivity as much as 40 times, making it capable of measuring small orthodontic force. The sensor design, fabrication, orthodontic stress measurement, and force reconstruction are given in details, and the experimental results demonstrate the feasibility of using miniaturized and ultra-thin sensors to determine the in vitro orthodontic forces. [ABSTRACT FROM PUBLISHER]

Inertial measurement units (IMUs) are widely used in motion measurement. However, the drift of IMUs results in significant accumulated errors for long-term position and orientation measurement. This paper reports a method to compensate the drift of inertial sensors with the assist of ultrasonic sensors and magnetometers. The magnetometer is combined with a three-axis accelerometer as a digital compass for orientation determination in static state by measuring the gravity and the earth's magnetic field vectors. A three-axis gyroscope is used to measure the orientation in dynamic state to complement the digital compass. Displacement determination is implemented using the accelerometer through double integration, and an ultrasonic sensor is employed to periodically calibrate the accumulated errors of the accelerometer. The redundant data from the multi-sensors are fused using extended Kalman filter (EKF), in which the position measured by the ultrasonic sensor and the orientation measured by the digital compass are defined as the observation values, and the position, velocity, and orientation are included in the state vector. Experimental results show that the accumulated errors of inertial sensors are reduced by ultrasonic sensors and magnetometers, and EKF improves the accuracy of orientation and position measurements. [ABSTRACT FROM PUBLISHER]

This paper presents the development of a piezoresistive stress sensor fabricated on silicon-on-insulator (SOI) wafers for measurement of electronic packaging stress at high temperature. The sensor consists of a series of sensor elements and calibration elements. The sensor elements comprise a 0°-90° p-type piezoresistor pair and a ±45° n-type piezoresistor pair for stress measurement, and the calibration elements comprise two polar three-piezoresistor rosettes with specific angels to calibrate the piezoresistive coefficients. The sensor and the calibration piezoresistors are etched from the SO! layer as separate "silicon islands" on the dielectric buried oxide (BOX) layer. This configuration exploits the excellent electrical insulation of the BOX layer, and enables high-temperature operation of the stress sensor by eliminating the leakage current. Design, fabrication, and the calibration of the piezoresistors at high temperatures show the feasibility of the SOI high-temperature stress sensor. The piezoresistive coefficients are calibrated versus stress and temperature, and the nonlinearity of the resistance versus temperature and the calibration errors are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents the design, fabrication, and characterization of a piezoelectric micromachined ultrasonic transducer (pMUT) operating in d33 mode. A piezoelectric PZT thin film is polarized along the in-plane direction using top square interdigital electrodes (IDEs), and the in-plane polarization and IDEs enable the pMUT to operate in d33 mode, which allows the PZT to convert the ultrasonic pressure-induced in-plane stresses into in-plane direction charges. The square IDEs fully exploit the stresses of the diaphragm to improve sensitivity and increase device capacitance, and the pMUT is optimized by varying the IDE dimensions rather than the thickness of the PZT film. Theoretical and finite-element analyses are performed to optimize the diaphragm and the IDE dimensions in terms of resonance frequency and sensitivity, respectively. The ultrasonic directivity of the pMUTs with different packaging configurations is characterized, showing large ultrasound inlet areas beneficial to ultrasonic applications requiring high directivity. [ABSTRACT FROM PUBLISHER]

This paper presents a novel silicon micromachining method, which combines tetra methyl ammonium hydroxide (TMAH) etching and deep-reactive ion etching (DRIE) along with bottom-up copper electroplating, to fabricate high-density and high-aspect ratio through-wafer electrical interconnects (TWEIs) for three-dimensional multichip packaging. The silicon wafer was locally etched with TMAH from the backside until the desired membrane thickness was reached, and then DRIE was performed on the membrane until the holes were etched through. TMAH etching preserved large areas of the wafers at the original thickness, thus, ensuring relatively strong mechanical strength and manipulability. DRIE made it possible to realize high-aspect ratio holes with minimized wafer area consumption. A new bottom-up copper electroplating technique was developed to fill the high-as-peer ratio through-wafer holes. This method can avoid seams and voids while achieving attractive electrical features. Through-wafer holes, as small as 5 μm in diameter, have been realized by using the combination of TMAH and DRIE, and have been completely and uniformly filled by using bottom-up copper electroplating. [ABSTRACT FROM AUTHOR]

This paper presents a method for measuring the complex permittivity of Ba0.5Sr0.5TiO3 (BST) ferroelectric thin films on a four-layered substrate at frequencies from 50 MHz to 26.5 GHz. Coplanar waveguide (CPW) lines are employed to measure the permittivity at high frequencies, whereas at low frequencies interdigital capacitors (IDCs) are used instead to avoid the calibration errors of CPW at those frequencies. A quasi-TEM transmission-line model and a lumped-element model, both on a four-layered substrate, are developed for CPW and IDC, respectively, using quasi-TEM analysis, conformal mapping, and partial-capacitance technique. The combinations of CPW model with measured transmission parameters and IDC model with measured scattering parameters allow extraction of the dielectric properties of the BST film. On-wafer through-reflect-line calibration is used to de-embed the true responses of the CPW lines. Dielectric constants of 400-600 and loss tangents of 0.05-0.1 are obtained at frequencies from 50 MHz to 26.5 GHz. [ABSTRACT FROM AUTHOR]

Test-analyze-and-redesign method is employed to develop a quartz crystal resonator (QCR) force and weight sensor with increased reliability for batch production. The sensor, which mainly consists of a QCR and a metal diaphragm structure, has the advantages of high resolution, digital output, and low cost. The failure mechanism of the single-diaphragm QCR sensor has been uncovered by experiments aiming at providing insight into the failure factors. In order to eliminate the failure stress and improve reliability, the sensor has been redesigned based on failure analysis results by designing a double-diaphragm structure. Life testing experiments for validating the effect of the corrective action show that reliability has been improved five times, and after redesign, the reliability satisfies the requirement of practical use. Accelerated life testing is performed to find acceleration factors and development stresses for batch production. [ABSTRACT FROM PUBLISHER]

This paper discusses the effect of transverse force on the performance of quartz crystal resonator (QXR) force sensors that use symmetrical incomplete circular QXRs as sensing elements. Based on Lee's vibration theory and the transverse force-induced stress distribution, frequency changes are derived. This result and finite element method (FEM) are applied to investigate the performance of two metal-quartz combined sensors under the action of transverse force. Analytical and experimental results show that transverse force affects the sensitivity and linearity of QXR force sensors. [ABSTRACT FROM AUTHOR]

An AT-cut thickness-shear quartz crystal resonator (QXR) has been used as a force sensing and self-temperature-sensing (STS) element to develop a digital output force sensor. The QXR is fixed in a two-line mounting configuration in a cylindrical metal shell by double diaphragms, through which a diametric force proportional to the unknown force is applied to the QXR. The double diaphragms improve the reliability and the mechanical stability of the sensor significantly. In order to increase the measurement range and the sensitivity, the energy trapping-based QXR is cut to a symmetrical, incomplete circular shape to decrease stress concentration. Because operating the QXR in dual-mode excitation allows the separation of force change effects from temperature change effects, force measurement and STS are accomplished simultaneously with the same QXR. The structure and the configuration are optimized with theoretical analysis and FEM. The dual-mode STS and temperature compensation are described in detail, as well as a trimming method to reduce activity dips of AT-cut QXRs. [ABSTRACT FROM PUBLISHER]

Discusses the changes in the resonance frequencies of the thickness-shear vibration of symmetrical incomplete circular AT-cut quartz crystal resonators. Formulation of two-dimensional motion equations to predict frequency changes; Stress distributions of symmetric incomplete AT-cut resonators; Equations used to calculate the force-frequency coefficients of incomplete circular resonators.

A wireless stress sensor integrated circuit (IC) has been implemented in 0.18 μm CMOS technology. The IC is composed of a 256-cell stress sensing array, the current-based sensor readout circuit, a 12 bit successive approximation (SAR) ADC and a 432 MHz wireless transmitter. The stress sensor employs orthogonally placed current source pair to measure the normal and shear stresses. The chip is backlapped to 35 μm for ultra-thin applications such as human skin stress distribution measurement. The measured sensing nonlinearity is below 0.7%. Experiments show that the implemented IC can be used to detect the facial expression changes. [ABSTRACT FROM AUTHOR]