-Shen Hsieh

A novel stress isolation guard-ring design for the improvement of a three-axis piezoresistive accelerometer

This study designs and implements a stress isolation guard-ring structure to improve the performances of the existing single proof-mass three-axis piezoresistive accelerometer. Thus, the environment disturbances, such as temperature variation and force/deflection transmittance, for a packaged three-axis piezoresistive accelerometer are significantly reduced. In application, the three-axis piezoresistive accelerometer has been fabricated using the bulk micromachining process on the SOI wafer. Experimental results show that the out-of-plane deformation of the suspended spring mass on the packaged accelerometer is reduced from 0.72 to 0.10 µm at a 150 °C temperature elevation. The temperature coefficient of zero-g offset for the presented sensor is reduced, and the temperature-induced sensitivity variation is minimized as well. Measurements also demonstrate that the guard-ring design successfully reduces the false signals induced by the force and displacement transmittance disturbances for one order of magnitude. Moreover, the three-axis acceleration sensing for the presented accelerometer with guard ring has also been demonstrated with sensitivities of 0.12–0.17 mV V−1 g−1 and nonlinearity < 1.02%.

Monolithic integration of capacitive sensors using a double-side CMOS MEMS post process

This study presents a novel double-side CMOS (complementary metal-oxide-semiconductor) post-process to monolithically integrate various capacitance-type CMOS MEMS sensors on a single chip. The CMOS post-process consists of three steps: (1) front-side bulk silicon etching, (2) backside bulk silicon etching and (3) sacrificial surface metal layers etching. Using a TSMC 2P4M CMOS process and the present double-side post-process this study has successfully integrated several types of capacitive transducers and their sensing circuits on a single chip. Monolithic integration of pressure sensors of different sensing ranges and sensitivities, three-axes accelerometers, and a pressure sensor and accelerometer are demonstrated. The measurement results of the pressure sensors show sensitivities ranging from 0.14 mV kPa−1 to 7.87 mV kPa−1. The three-axes accelerometers have a sensitivity of 3.9 mV G−1 in the in-plane direction and 0.9 mV G−1 in the out-of-plane direction; and the accelerated measurement ranges from 0.3 G to 6 G.

A novel stress isolation guard ring design for the improvement of three-axis piezoresistive accelerometer

This study designs and implements a stress isolation guard-ring structure to improve the performances of the existing single proof-mass 3-axis piezoresistive accelerometer. Thus, the environment disturbances (temperature variation and force/deflection transmittance) for such packaged 3-axis piezoresistive accelerometer are significantly reduced. Measurements demonstrate the guard-ring design successfully reduce the false signals (induced by temperature variation and force/displacement transmittance) for one order of magnitude. Moreover, the proposed accelerometer still maintains the advantages of existing design, such as single proof-mass for 3-axis acceleration sensing, and better linearity. Sensitivities of present accelerometer range 0.127∼1.77mV/G/V and non-linearity&#60;1.02%VFSS.

A novel inverse-magnetostrictive type pressure sensor with planar sensing inductor

In this study, a novel planar inductor to detect the pressure sensor is proposed. The planar inductor consists of planar coil and CoFeB films. The proposed sensor exploits the inverse-magnetostriction effect to change the permeability of the CoFeB film by pressure load. This permeability variation will further result in the inductance difference of the planar inductor. Consequently the relationship between the pressure and inductance can be obtained by the inductance measurement. To demonstrate the presented concept, prototype inverse-magnetostrictive type pressure sensors with planar sensing inductor (Al planar coil and CoFeB films) have been implemented and tested. Sensitivity measurements show the gauge factor of the novel pressure sensor is approximate 280. To support the proposed concept, the vibrating sample magnetometer (VSM) measurements show the magnetic anisotropy of the CoFeB film (extracted from the hysteresis loops) is changed due to the applied pressure load.

Wireless magnetostrictive type inductive sensing CMOS-MEMS pressure sensors

This study demonstrates the wireless magnetostrictive type inductive sensing CMOS-MEMS pressure sensors using the TSMC 0.18μm 1P6M process. Features of this study are: (1) High sensitivity pressure sensors are realized based on the inverse-magnetostrictive sensing principle; (2) metal and dielectric layers of CMOS process are employed to form the magnetic coil and sensing diaphragm respectively; (3) additional magnetostrictive CoFeB film was deposited and patterned by the shadow sputtering; (4) wireless sensing is available by the external reading coil. Experiments show sensors with gauge-factor ranging 480~1100 are achieved, and wireless sensing capability is also demonstrated.

Magnetostrictive type tactile sensor based on metal embedded polymer architecture

This study presents new process scheme to fabricate polymer structure with embedded metal on silicon substrate. The primary merit of presented process scheme is: simple approach for the integration of 3D structures with different materials (e.g. metal, glass, polymer) on substrate. To demonstrate the feasibility of the proposed process scheme, a tactile sensor design consisting of polymer structure with embedded 3D Ni coil winding is implemented. As the polymer diaphragm deformed by tactile force, the magnetostriction effect of the 3D Ni coil inductor will induce the permeability change. Thus, the permeability change as well as the tactile force can be detected by the inductance variation. Preliminary measurements show the sensitivity of magnetostrictive type tactile sensor based on the proposed metal embedded polymer architecture is near 1.33%/N at the sensing range of 0~1N.

Designs of planar sensing inductor on inverse-magnetostrictive type pressure sensor

This study presents a pressure sensor design which consisted of the planar coil and CoFeB magnetic films. As the Si diaphragm deformed by pressure load, the magnetostriction effect of magnetic film will cause the permeability change of CoFeB. Thus, the permeability change as well as the pressure load can be detected by the inductance difference of the planar inductor. The proposed magnetostrictive pressure sensor with planar sensing inductor had been implemented and tested in the previous work. In this study, the design of planar sensing inductor is further investigated and reported. Based on the design modification of planar sensing inductor, such as coil turns or the geometry of magnetic film, the sensitivity could be improved successfully. Preliminary measurements demonstrate a high gauge factor of near 850 can be achieved through the inverse-magnetostrictive type pressure sensor.

Study and characterization of plastic encapsulated package for a three-axis piezoresistive acceleromete with guard-ring structure

This study reports the performance of a three-axis piezoresisitvie accelerometer with a guard-ring structure after plastic packaging. The accelerometers, with and without guard-ring structure, are capped with glass substrate to form the glass/Si/glass sandwich and then encapsulated in plastic package. The testing results on these packaged accelerometers have shown that the guard-ring structure successfully suppresses the performance shift caused by plastic package for one order of magnitude. The glass/Si/glass sandwich structure adds air damping to the accelerometer, hence its resonant frequency is slightly reduced (less than 0.5%). Moreover, the guard-ring structure has relatively large stiffness and is considered as a rigid body, and its influence on the sensor dynamics can be ignored. In conclusion, the guard ring structure significantly reduces the performances variation of packaged sensor. Thus, the inexpensive plastic encapsulated package for accelerometers can be implemented on the real products.

Piezoresistive pressure sensor with Ladder shape design of piezoresistor

In this study, a novel piezoresistor (PZR) design to improve the sensitivity of the piezoresistive type pressure sensor is reported. In this design, the PZR combined with various doping concentrations and doping depths is proposed and implemented. According to the design concept, the combined PZR which includes multiple piezoresistance coefficients would be arranged in a unique shape, just like a ladder. Theoretically, the sensitivity improvement could boost up to 15% based on this PZR design, even under the conditions of membrane edge offset due to fabrication processes. As a result, the sensitivity of the pressure sensor which adopted the Ladder shape PZR design is 0.058 mV/V/kPa. Moreover, the doping profile of the Ladder shape PZR is also extracted by SIMS. The serial measurements successfully prove the feasibility of this design concept. In the future, the presented PZR design can be further extended to various piezoresistive sensors, such as accelerometer, gyro, etc.

Method for performance improvement and size shrinkage of a three-axis piezoresistive accelerometer with guard-ring structure

A stress isolation guard-ring to reduce the unwanted signals induced by the environmental disturbances for a packaged three-axis piezoresistive accelerometer is proposed [1-2]. This study further reports an optimum design to shrink the size of guard-ring, yet maintain the performance of accelerometer. The commercial finite element analysis (FEA) software, CoventorWare, is employed to evaluate the candidate designs of sensors. The Taguchis optimum design method is further employed to improve the sensor performances under environment disturbances and to shrink the size of the stress isolation structure. Based on the results, the performance of the accelerometer is improved both in offset shift and sensitivity shift for one order of magnitude, and the size of the stress isolation structure (the sum of guard-ring length/width and connection bridge length) has been shrunk for 29% (from 138 μm to 98 μm). Moreover, the unwanted higher vibration modes are far away from the first three modes. The proposed accelerometer design keeps the advantages of the original three-axis accelerometer design.