Complementary Metal Oxide Semiconductor MEMS Research Articles

Research on a CMOS-MEMS Infrared Sensor with Reduced Graphene Oxide

In this research, a new application of reduced graphene oxide (rGO) for a complementary metal-oxide-semiconductor (CMOS)-MEMS infrared (IR) sensor and emitter is proposed. Thorough investigations of IR properties including absorption and emission were proceeded with careful calibration and measurement with a CMOS thermoelectric sensor. The thermocouples of the sensor consist of aluminum and n-polysilicon layers which are fabricated with the TSMC 0.35 μm CMOS process and MEMS post-process. In order to improve the adhesion of rGO, a sensing area at the center of the membrane is formed with an array of holes, which is easy for the drop-coating of rGO material upon the sensing region. To evaluate the performance of the IR sensor with rGO, different conditions of the IR thermal radiation experiments were arranged. The results show that the responsivity of our proposed CMOS-MEMS IR sensor with rGO increases by about 77% compared with the sensor without rGO. For different IR absorption incident angles, the measurement of field of view shows that the CMOS-MEMS IR sensor with rGO has a smaller view angle, which can be applied for the application of long-distance measuring. In addition, characteristics of the proposed thermopile are estimated and analyzed with comparisons to the available commercial sensors by the experiments.

A Closed-Loop Controlled CMOS MEMS Biaxial Scanning Mirror for Projection Displays

This work presents a biaxial electromag- netically-driven piezoresistively sensed scanning mirror fabricated in a CMOS (complementary metal oxide semiconductor) process. The structure containing the CMOS metal/dielectric layers and underlying silicon is released after back- and front-side etch. The drive coil and piezoresistive sensors are implemented by the metal and polysilicon thin films. Biaxial resonances at 1.13 kHz and 41.5 kHz, and an optical angle of 50° for horizontal scan under a drive current of 12.5 mA are measured. Closed-loop control and oscillation for vertical and horizontal scans are also demonstrated for practical applications.

Development of CMOS MEMS inductive type tactile sensor with the integration of chrome steel ball force interface

This study presents an inductive tactile sensor with a chrome steel ball sensing interface based on the commercially available standard complementary metal–oxide–semiconductor (CMOS) process (the TSMC 0.18 µm 1P6M CMOS process). The tactile senor has a deformable polymer layer as the spring of the device and no fragile suspended thin film structures are required. As a tactile force is applied on the chrome steel ball, the polymer would deform. The distance between the chrome steel ball and the sensing coil would changed. Thus, the tactile force can be detected by the inductance change of the sensing coil. In short, the chrome steel ball acts as a tactile bump as well as the sensing interface. Experimental results show that the proposed inductive tactile sensor has a sensing range of 0–1.4 N with a sensitivity of 9.22(%/N) and nonlinearity of 2%. Preliminary wireless sensing test is also demonstrated. Moreover, the influence of the process and material issues on the sensor performances have also been investigated.

Design and Characterization of a CMOS MEMS Capacitive Oscillator for Resonant Sensing in Liquids

Liquid properties can be studied through monitoring the in-liquid resonant behavior of micromechanical oscillators. This paper presents the first attempt to implement capacitively transduced micromechanical oscillators in a complementary metal-oxide-semiconductor (CMOS) process for in-liquid operation. The parallel-plate drive and sense capacitors have a 2-μm gap and 1-μm dielectric sidewalls to protect the electrodes. A wide-range CMOS phase-locked-loop circuit is designed to sustain oscillation in face of the large resonance shift while operating in liquids. Measurements show that the capacitive micro-resonator is driven to oscillation at 51.2 kHz in air. The resonant frequency increases to 78.1, 121.9, and 203 kHz in ethanol, isopropyl alcohol, and deionized water, respectively, due to the elastic squeeze-film damping effect and individual liquid properties. The large resonance shift in liquids can be utilized for sensitive bio/chemical detection in the future.

Characterization of CMOS MEMS Capacitive Ultrasonic Sensors for Fast Photoacoustic Imaging

This work proposes to develop a CMOS (complementary metal oxide semiconductor) capacitive ultrasonic sensor chip that can be jointly operated with an acoustic lens system to achieve fast 3-D photoacoustic imaging. Compared to conventional piezoelectric technology, capacitive transducers have a wider bandwidth and can be miniaturized and fabricated in a dense array to provide better imaging quality. Different from our previous approach that requires a long acquisition time to measure the complete waveform of each sensor for 3-D image reconstruction, the new scheme only has to detect the peak amplitude of a waveform. This paper reports the characterization of the fabricated sensors, which shows the sensors have a resonant frequency near 3.5 MHz and the peak detection errors are typically within ±10% for test signals from 1 to 10 MHz with the amplitude from 50 to 400 mV.

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 capacitive humidity sensor integrated with micro heater and ring oscillator circuit fabricated by CMOS–MEMS technique

This study presents the fabrication of a humidity sensor with a micro heater and a ring oscillator circuit using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process. The micro heater is utilized to provide a super-ambient working temperature to the humidity sensor, which can avoid the humidity sensor to generate the signal drift. The humidity sensor is a capacitive type sensor. The structure of the humidity sensor consists of interdigital electrodes and a sensing film. The sensing film, which is polyimide, is coated on interdigital electrodes. The humidity sensor changes in capacitance when the sensing film absorbs or desorbs water vapor. The ring oscillator circuit is employed to convert the capacitance of the humidity sensor into the oscillation frequency output. Experimental results show that the sensitivity of the humidity sensor is about 25.5 kHz/% RH at 80 °C.