Jiachou Wang

A silicon integrated micro nano-positioning XY-stage for nano-manipulation

An integrated micro XY-stage with a 2 × 2 mm2 movable table is designed and fabricated for application in nanometer-scale operation and nanometric positioning precision. The device integrates the functions of both actuating and sensing in a monolithic chip and is mainly composed of a silicon-based XY-stage, comb-drive actuator and a displacement sensor, which are developed by using double-sided bulk-micromachining technology. The high-aspect-ratio comb-driven XY-stage is achieved by deep reactive ion etching (DRIE) on both sides of the wafer. The displacement sensor is formed on four vertical sidewall surface piezoresistors with a full Wheatstone bridge circuit, where a novel fabrication process of a vertical sidewall surface piezoresistor is proposed. Comprehensive design and analysis of the comb actuator, the piezoresistive displacement sensor and the XY-stage are given in full detail, and the experimental results verify the design and fabrication of the device. The final realization of the device shows that the sensitivity of the fabricated piezoresistive sensors is better than 1.17 mV µm−1 without amplification, and the linearity is better than 0.814%. Under 28.5 V driving voltage, a ±10 µm single-axis displacement is measured without crosstalk and the resonant frequency is measured at 983 Hz in air.

Monolithic Integration of Pressure Plus Acceleration Composite TPMS Sensors With a Single-Sided Micromachining Technology

This paper concerns the development of a single-side micromachined tire-pressure monitoring system (TPMS) sensor for automobiles, which is with a piezoresistive pressure sensor and a cantilever-mass piezoresistive accelerometer monolithically integrated in a 1.6 mm × 1.5 mm sized (111)-silicon chip. Single-wafer-based front-side silicon micromachining and metal electroplating technologies are employed to fabricate the device. Specially designed releasing trenches along (111) orientation are constructed to form the hexagonal pressure-sensitive diaphragm and the postsealed vacuum reference cavity. The fabrication of the accelerometer is also based on a hexagonal diaphragm that is latterly cut into suspended cantilevers and seismic mass. To achieve a high sensitivity, a high-density copper thick film is selectively electroplated to significantly increase the mass. The performance of the 115-g-ranged accelerometer is measured, exhibiting a sensitivity of 99.9 μV/g (under 3.3-V supply), nonlinearity of ±0.45% FS, and the noise floor of better than 0.2 g. The 750-kPa-ranged pressure-sensor sensitivity is measured as 0.108 mV/kPa (under 3.3-V supply), with the nonlinearity error smaller than ±0.1% FS and the temperature coefficient of sensitivity as -0.19%/°C FS before compensation. The noise floor of the pressure-sensor out- put signal is 0.15 kPa. The zero-point temperature coefficient is tested as -0.11%/°C FS and -0.024%/°C FS for the accelerometer and the pressure sensor, respectively. Fabricated with the low-cost front-side micromachining technique, the small-sized TPMS sensors are promising in practical applications and volume production.

A High-Performance Dual-Cantilever High-Shock Accelerometer Single-Sided Micromachined in (111) Silicon Wafers

A single-side processed dual-cantilever high-shock accelerometer in (111) silicon wafers is proposed in this paper. The device is formed by using advanced silicon surface and bulk micromachining technologies, including deep-reactive ionic etch and lateral under-etching structural release. Because the sensor is fabricated in (111) silicon wafer and has a single-chip single-side structure, it facilitates simple post-packaging, reduced device dimension, and low cost mass production. The controllable gap distance between the bottom surface of the cantilever and the substrate can be used for restraining cross-sensitivity of orthogonal direction. The performance of the accelerometer is examined by using a free dropping hammer system. The results of the shock test show the acceleration sensitivity of 0.71 μVg-1 for a 20 500 g shock acceleration under 3.3 V power supply and the resonant frequency of 79 kHz. The zero-point offset temperature drift of the sensor is 89 within the temperature range of to 120 .

Single-Side Fabricated Pressure Sensors for IC-Foundry-Compatible, High-Yield, and Low-Cost Volume Production

In this letter, a new low-cost and high-yield manufacturing technique for volume production of pressure sensors is proposed and developed. The IC-foundry-compatible process is conducted only from the front side of (111) silicon wafers, without double-sided alignment exposure, wafer bonding, and double-sided polished wafers needed. With the single-wafer-based single-side bulk-micromachining technique, the sensor chip size is as small as 0.6 mm × 0.6 mm that facilitates low-cost high-throughput IC-foundry batch fabrication. Compared with the conventional double-sided micromachining approach where the pressure-sensing diaphragm thickness is determined by back-side deep etching, the front-side micromachining scheme uses front-side shallow etching that provides more precise and uniform control to the thickness for higher yield. 0.087-mV/kPa sensitivity and ±0.09%FS nonlinearity are measured for the fabricated 750-kPa range sensor, and the temperature coefficient of offset ( TCO) is as low as -0.032%/ °C ·FS. With the new technique, the sensors are promising in automotive and consumer electronics applications.

Fully front-side bulk-micromachined single-chip micro flow sensors for bare-chip SMT (surface mounting technology) packaging

This paper reports novel single-wafer-based piezoresistive micro flow sensors, which are bulk micromachined only from the front side of the silicon wafer to facilitate the sensor-bare chips directly packaged into micro-fluidic systems with low-cost surface mounting technology (SMT). With neither double-sided micromachining nor multiwafer bonding needed, two structural types of the piezoresistive flow sensors are designed and fabricated in (1 1 1) wafers, where ‘type A’ sensor has a smaller channel cross section area compared to ‘type B’ sensor. After the bare sensor chip directly attached on a printed circuit board (PCB), wire bonded between the pads and the PCB for electric interconnection and the inlet/outlet front side connected, deionized water is flowed into the both types of flow sensors to characterize piezoresistive output of the differential pressure sensing elements in terms of the flow rate. For ‘type A’ and ‘type B’ sensors that are both power supplied with DC 5 V, the sensitivities are sequentially measured as 766.80 mV (µL s−1)−1 and 19.12 mV (µL s−1)−1, with the nonlinearities as 0.4% FS and 0.9% FS, respectively. Compared with traditionally fabricated micro flow sensors, the single-chip fabricated differential-pressure flow sensors can be low-cost volume manufactured. Moreover, the bare sensor chips can be simply SMT packaged for low-cost micro-system applications.

A Tri-Beam Dog-Bone Resonant Sensor With High-

This paper presents a novel tri-beam structured dog-bone resonance-mode micro-sensor, with a frequency readout piezoresistive Wheatstone-bridge independently located at the central beam for the detection of liquid-phase bio/chemical analyte. Compared with the conventional dual-beam dog-bone resonator, the tri-beam resonator has advantages in the elimination of signal feed-through and high-Q resonance in liquid. With sensing-material loaded on the sensing-plates of the resonator, the tri-beam extension-mode resonator is developed for liquid-phase sensing to adsorbed mass. Attributed to the high-Q factor in solution, the resonant sensor is suitable for the detection of trace-amount bio/chemical liquid-droplet sample. The experimental results show that the aqueous Hg2+ ion of 500 ppb concentration can be detected.

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Monolithic integration of micromechanical composite sensors needs to fabricate multiple levels of three-dimensional (3-D) microstructures to satisfy individual requirements from individual onchip sensing elements. Meanwhile, volume fabrication of the composite sensors is needed in many applications that prefer single-sided process in low-cost non-silicon-on-insulator single wafer. A novel single-sided micromachining technique is herein proposed and developed to form such multilevel 3-D structures, where only integrated-circuit (IC) foundry available processes are used, i.e., neither double-sided process nor wafer-bonding is used. With the IC-foundry compatible micromachining process, a six-level 3-D microstructure has been successfully formed for tire-pressure monitoring system (TPMS) sensors. Benefited from the single-side process and the namely pressure-sensor in accelerometer (PinG) dual-sensor architecture, the single-wafer-based dual-sensor features a tiny chip size of 1.25 mm × 1.25 mm × 0.45 mm. Supplied with 3.3 V, 0.1-mV/kPa sensitivity for the 500-kPa-ranged pressure sensor and 0.05-mV/g sensitivity for the 120-g-ranged accelerometer are measured. By freely suspending the pressure-sensor structure from the stress-free mass end, the influence of acceleration to the pressure sensor is well eliminated, which was the main problem of the previous PinG sensors. Besides the achieved high-performance TPMS dual sensor, the IC-foundry manufacturable technique for multilevel 3-D microelectromechanical systems (MEMS) structures can be widely used in various monolithic MEMS devices.

in Liquid for Disposable Test-Strip Detection of Analyte Droplet

This paper presents a novel single-wafer-based single-sided bulk-micromachining piezoresistive pressure sensor that features highly uniform diaphragm thickness and ultra-small size. Without double-side alignment and wafer bonding needed, the single-crystalline silicon piezoresistive pressure sensors can be volume manufactured in standard IC-foundries with ultra-low fabrication cost for applications of consumer electronics. The pressure sensor sensitivity range 750KPa is about 0.033mV/V/KPa and the non-linearity is less than ±0.1%·FS. Even though the two rows of opening holes are embedded in the silicon diaphragm, the tested zero-point temperature coefficient as low as −0.022%/ °C · FS (−40°C to +120°C) indicates no obvious influence to the sensor stability.

Single-Side Fabrication of Multilevel 3-D Microstructures for Monolithic Dual Sensors

For the first time, the study proposes and develops a MEMS process of TUB (thin-film under bulk) to develop a novel MEMS configuration, where a surface-micromachined poly-Si thin-film is constructed under a bulk-micromachined single-crystalline silicon (SC-Si) layer. The TUB process can be performed in standard IC-foundry to volume fabricate complex-structured MEMS devices in single (111)-silicon wafer. As the first application example of the TUB technology, piezoresistive pressure sensors for low range measurement are developed. The low-range pressure sensors have been high-yield fabricated, with the tiny chip size of 1.2mm by 1.2mm. Thanks to the proposed TUB process where etching stop is realized for removing CS-Si but retaining poly-Si, the complex sensor structure of CS-Si beam-island reinforced poly-Si thin-diaphragm can be uniformly fabricated (see Figure 1). The CS-Si beam-mass reinforced poly-Si diaphragm well restricts large deflection induced nonlinear output signal, while the stress concentration effect on the CS-Si secures piezoresistive sensitivity to pressure. With the piezoresistive Wheatstone-bridge integrated in the CS-Si beam, high-performance piezoresistive output signal is achieved. The fabricated pressure sensor exhibits sensitivity of 13.36mV/kPa before amplification and low nonlinearity of 0.3%, thereby providing sub-kPa range applications like distributed outlet monitoring of central air-conditional system. The bulk/surface combined micromachining process is promising for various complex MEMS structures.

A single-wafer-based single-sided bulk-micromachining technique for high-yield and low-cost volume production of pressure sensors

Presented in this paper is a novel kinetic energy-harvester that can autonomously sense sub-g acceleration-level vibration under non-power-supply situation. Only when the vibration-amplitude reaches the pre-set threshold, the device is switched on to generate electric energy, otherwise the device keeps idle. Asymmetric vertical magnetic-force coupling between two vibration stages is designed between a low-frequency ‘Stage-1’ micro-cantilever for response to environmental vibration and a high-frequency ‘Stage-2’ piezoelectric-cantilever for resonant electric-generation. The coupling effect between the magnet on Stage-1 and the ferromagnetic-material made Stage-2 can effectively sharpen up the change of the vertical magnetic coupling force. The sharpened magnetic-interaction induces high vibration velocity and efficient electricity generation of Stage-2, even when the harvester is excited by sub-g weak vibration. After analysis for the asymmetric dual-stage interaction, three devices with the thresholds ranged from 0.15g to 0.55g are fabricated and tested, resulting in agreement with design. The pre-settable threshold can be varied by adjusting the mass attached on Stage-1. The electric-generation action is accurately triggered when the threshold is reached, with the switching tolerance narrower than 0.05g. This sensing/generating dual-functional device is promising for simultaneously acquiring weak environmental vibration information and simultaneous electric-generation for power-supply to the sensing-signal processing system. The dual-functional device is promising to be developed as a self-powered pedometer to replace the conventional ones where batteries have been always needed.