Chih-Ming Sun

Implementation of a Monolithic Single Proof-Mass Tri-Axis Accelerometer Using CMOS-MEMS Technique

This paper presents a novel single proof-mass tri-axis capacitive type complementary metal oxide semiconductor-microelectromechanical system accelerometer to reduce the footprint of the chip. A serpentine out-of-plane (Z-axis) spring is designed to reduce cross-axis sensitivity. The tri-axis accelerometer has been successfully implemented using the TSMC 2P4M process and in-house postprocessing. The die size of this accelerometer chip containing the MEMS structure and sensing circuits is 1.78 × 1.38 mm, a reduction of nearly 50% in chip size. Within the measurement range of ~0.8 6G, the tri-axis accelerometer sensitivities (nonlinearity) of each direction are 0.53 mV/G (2.64%) for the X-axis, 0.28 mV/G (3.15%) for the Y-axis, and 0.2 mV/G (3.36%) for the Z-axis, respectively. In addition, the cross-axis sensitivities of these three axes range from 1% to 8.3% for the same measurement range. The noise floors in each direction are 120 mG/rtHz for the X-axis, 271 mG/rtHz for the Y-axis, and 357 mG/rtHz for the Z-axis.

Design and application of a metal wet-etching post-process for the improvement of CMOS-MEMS capacitive sensors

This study presents a process design methodology to improve the performance of a CMOS-MEMS gap-closing capacitive sensor. In addition to the standard CMOS process, the metal wet-etching approach is employed as the post-CMOS process to realize the present design. The dielectric layers of the CMOS process are exploited to form the main micro mechanical structures of the sensor. The metal layers of the CMOS process are used as the sensing electrodes and sacrificial layers. The advantages of the sensor design are as follows: (1) the parasitic capacitance is significantly reduced by the dielectric structure, (2) in-plane and out-of-plane sensing gaps can be reduced to increase the sensitivity, and (3) plate-type instead of comb-type out-of-plane sensing electrodes are available to increase the sensing electrode area. To demonstrate the feasibility of the present design, a three-axis capacitive CMOS-MEMS accelerometers chip is implemented and characterized. Measurements show that the sensitivities of accelerometers reach 11.5 mV G−1 (in the X-, Y-axes) and 7.8 mV G−1 (in the Z-axis), respectively, which are nearly one order larger than existing designs. Moreover, the detection of 10 mG excitation using the three-axis accelerometer is demonstrated for both in-plane and out-of-plane directions.

A novel CMOS out-of-plane accelerometer with fully differential gap-closing capacitance sensing electrodes

This study presents a novel CMOS-MEMS out-of-plane linear accelerometer. This capacitance-type accelerometer contains specially designed gap-closing sensing electrode arrays with on-chip fully differential sensing circuits. Moreover, the comb-finger electrodes have the characteristics of the high fill factor and sub-micron gap to increase the sensing capacitance. Thus, the sensitivity and signal-to-noise ratio can be further improved. This study has established a post-CMOS wet-etching process to realize the accelerometer with sensing electrodes of the sub-micron gap in the out-of-plane direction. The present accelerometer has been demonstrated using the standard TSMC 2P4M process plus the post-release technique. The measurement results demonstrate that the accelerometer has a sensitivity of 1.14 mV g −1 , and a nonlinearity of 3.4%. (Some figures in this article are in colour only in the electronic version)

Development of a CMOS-Based Capacitive Tactile Sensor With Adjustable Sensing Range and Sensitivity Using Polymer Fill-In

This paper reports a capacitive-type CMOSmicroelectromechanical system tactile sensor containing a capacitance-sensing gap filled with polymer. Thus, the equivalent stiffness of the tactile sensor can be modulated by the polymer fill-in, so as to further tune its sensing range. Moreover, the polymer fill-in has a higher dielectric constant to increase the sensitivity of the tactile sensor. In short, the sensing range and sensitivity of the proposed tactile sensor can be easily changed by using the polymer fill-in. In application, the tactile sensor and sensing circuits have been designed and implemented using the 1) TSMC 0.35 μm 2P4M CMOS process and the 2) in-house post-CMOS releasing and polymer-filling processes. The polydimethylsiloxane (PDMS) material with different curing agent ratios has been exploited as the fill-in polymers. The experiment results demonstrate that the equivalent stiffness of tactile sensors can be adjusted from 16.85 to 124.43 kN/m. Thus, the sensitivity of the tactile sensor increases from 1.5 to 42.7 mV/mN by varying the PDMS filling. Moreover, the maximum sensing load is also improved.

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 monolithic 3D fully-differential CMOS accelerometer

This study presents a novel inertia sensor design to monolithic integrate x, y, and z-axis accelerometers on a single chip. The chip is implemented using the TSMC 0.35 mum 2P4M CMOS process, and post metal wet-etching and dielectric dry-etching processes. Thus, the fully-differential capacitance sensing in-plane and out-plane CMOS accelerometers are realized. The measurement results demonstrate the sensitivities for in-plane and out-of-plane accelerometers are 3.9 mV/G and 0.9 mV/G, respectively. The coupling ratios for in-plane and out-plane accelerometer are 3~5% and 15~30%, respectively.

Implementation of fully-differential capacitance sensing accelerometer using glass proof-mass with Si-vias

This study presents a novel fully-differential capacitive sensing accelerometer design consisting of glass proof-mass and Si-vias. The accelerometer with glass proof-mass has three merits, (1) the insulation glass proof-mass and conducting Si vias enable the gap-closing fully-differential electrodes design, (2) the electrical routings on insulation glass proof-mass can reduce parasitic capacitance, (3) the proof-mass is significantly increased by the nearly whole wafer thick glass material. In application, the fully-differential accelerometer with glass proof-mass is fabricated and characterized. The preliminary measurement results demonstrate the sensitivity of accelerometer is 14.44mV/G with a nonlinearity of 4.91%.

A novel double-side CMOS-MEMS post processing for monolithic sensor integration

This study presents a novel double-side CMOS post-process to monolithically integrate various capacitance type CMOS sensors on a single chip. In applications, the pressure sensor and linear accelerometer have been realized and monolithic integrated using the TSMC 2P4M process and the present post-process. The measurement results show that sensitivities (non-linearity) of the pressure sensor and the accelerometer are 12 mV/kPa (4.77%), and 3.9 mV/G (1.06%), respectively. The measurement ranges are 0~10 kPa, and 0.3~6 G, respectively.

Development of CMOS-MEMS in-plane magnetic coils for application as a three-axis resonant magnetic sensor

This study designs and implements a single unit three-axis magnetic sensor using the standard TSMC 0.35??m 2P4M CMOS process. The magnetic sensor consists of springs, a proof-mass with embedded magnetic coils, and sensing electrodes. Two sets of in-plane magnetic coils respectively arranged in two orthogonal axes are realized using the stacking of metal and tungsten layers in the CMOS process. The number of turns for the proposed in-plane magnetic-coil is not restricted by the space and thin film layers of the CMOS process. The magnetic coils could respectively generate Lorentz and electromagnetic forces by out-of-plane and in-plane magnetic fields to excite the spring?mass structure. Capacitance sensing electrodes could detect the dynamic response of the spring?mass structure to determine the magnetic fields. Measurements indicate the typical sensitivities of the sensor are 0.21??V??T?1?(x-axis), 0.20??V ?T?1?(y-axis), and 0.90??V??T?1?(z-axis) at 1 atm. Moreover, the resolutions of the sensor are respectively 384 nT rtHz?1?for the x-axis, 403?nT?rtHz?1?for the y-axis, and 62 nT rtHz?1?for the z-axis at 1 atm. The presented magnetic sensor could monolithically integrate with other CMOS-MEMS devices for various applications.

A 400×400µm 2 3-axis CMOS-MEMS accelerometer with vertically integrated fully-differential sensing electrodes

This study presents a novel CMOS-MEMS 3-axis accelerometer design using TSMC 0.18µm 1P6M CMOS process. Thus, the footprint size of 3-axis accelerometer is significantly reduced to 400×400µm2 by the single proof-mass design, Due to the novel fully-differential gap-closing sensing electrode design in all three sensing directions, the sensitivities of 3-axis accelerometer are improved. Moreover, by means of metal wet-etching post-CMOS process, very small in-plane and out-of-plane sensing gaps are respectively defined by the minimum line width and one metal-layer thickness of TSMC process. Thus, the sensitivity of accelerometer is further improved. Table1 summarize the measured performances of proposed accelerometer, which indicates its chip size and performances are better than existing designs.