This paper reports a CMOS BioMEMS (biological micro-electromechanical system) platform for monolithically integrated multi-type biosensors and readout circuits. Gold is implemented in the current CMOS MEMS platform as an absorption layer for bio targets by wafer-level process tools. The characteristics of the gold and piezoresistive cantilever structures are analyzed. Two kinds of biosensors are fabricated and investigated in this work. The first one is an electro-microchip for immunoassay using platinum nano-particles and silver enhancement, and the detection time is over 10% shorter than the previous example made with a glass platform. The second biosensor is composed of the MIP (molecularly imprinted polymer) and ion-sensitive field-effect transistor (ISFET), and is used to detect creatinine. Moreover, the ring-oscillator-based readout circuit integrated with the ISFET is able to report the creatinine concentration. Two experimental cases demonstrate the possibility of integrating multiple type biosensors and readout circuits in micro or nano systems based on the CMOS BioMEMS platform.

Multiple type biosensors fabricated using the CMOS BioMEMS platform

This paper describes the design, fabrication and characterization of a complementary metal-oxide-semiconductor (CMOS) micro-electro-mechanical-system (MEMS) accelerometer implemented in a 0.18 µm multi-project wafer (MPW) CMOS MEMS process. In addition to the standard CMOS process, an additional aluminum layer and a thick photoresist masking layer are employed to achieve etching and microstructural release. The structural thickness of the accelerometer is up to 9 µm and the minimum structural spacing is 2.3 µm. The out-of-plane deflection resulted from the vertical stress gradient over the whole device is controlled to be under 0.2 µm. The chip area containing the micromechanical structure and switched-capacitor sensing circuit is 1.18 × 0.9 mm2, and the total power consumption is only 0.7 mW. Within the sensing range of ±6 G, the measured nonlinearity is 1.07% and the cross-axis sensitivities with respect to the in-plane and out-of-plane are 0.5% and 5.8%, respectively. The average sensitivity of five tested accelerometers is 191.4 mV G−1with a standard deviation of 2.5 mV G−1. The measured output noise floor is 354 µG Hz−1/2, corresponding to a 100 Hz 1 G sinusoidal acceleration. The measured output offset voltage is about 100 mV at 27 °C, and the zero-G temperature coefficient of the accelerometer output is 0.94 mV °C−1 below 85 °C.

http://iopscience.iop.org/article/10.1088/0960-1317/22/5/055010/pdf

Implementation of a monolithic capacitive accelerometer in a wafer-level 0.18 µm CMOS MEMS process

Frequency modulation technique can be applied to microelectromechanical systems (MEMS) transducers that require some form of resistive sensing. For example, electrothermal sensing is being investigated as a viable means of measuring displacement in micromachined transducers. This paper proposes a highly sensitive readout circuit, which can convert 10 Ω change of resistance in a 400 Ω electrothermal sensor to more than 200 kHz frequency variation (350-550 KHz). The frequency variations are then converted to voltage values by means of a frequency demodulation. In addition, the proposed technique achieves high linearity from the voltage applied to the actuator to the voltage measured at the sensor's output, which can potentially eliminate the need for an additional linearization if the sensor is used in a feedback loop. The proposed approach leads to high sensitivity in the MEMS electrothermal sensing since the method is not affected by amplitude variations that could arise from the readout circuit.

Frequency Modulation Technique for MEMS Resistive Sensing

This paper presents a digital trimming technique for canceling the output offsets caused by sensor mismatches in an accelerometer design. The offset cancellation techniques provide fine trimming steps with higher chip area efficiency compared with that of conventional capacitor array compensation approaches. The accelerometer, fabricated in a 0.18- μm complementary metal-oxide-semiconductor micro-electro-mechanical-system process, containing the micro-mechanical structure and readout circuits, occupies only a 0.64 × 0.9 mm2 area. The chip draws 0.4 mA from a 1.8-V supply. The measured sensitivity is 195 mV/g and the nonlinearity is 0.78% within the ±12 g sensing range. The output noise floor is 150 μg/√{Hz}, corresponding to a 1-g 100-Hz sinusoidal acceleration. The output offset voltage can be trimmed from several tens to several hundreds of millivolts down to several millivolts.

Digital Offset Trimming Techniques for CMOS MEMS Accelerometers

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.

https://www.mdpi.com/1424-8220/20/14/4007/pdf

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

This work presents the design and characterization of a CMOS-integrated thermal sensor that features a novel oscillator-based sensing interface to achieve a high thermoelectric sensitivity. The thirty pairs of thermocouples are made of n+/p+ polysilicon of a standard 0.18-mum CMOS to produce a large thermoelectric voltage. The produced thermoelectric voltage is used to control the bias current of a high-frequency oscillator circuit and causes a shift in the output frequency. Experimental result indicates the 544-MHz oscillator has a temperature sensitivity of 46.3 kHz/degC.

/pdf/a-cmos-mems-thermal-sensor-with-high-frequency-output-315ipaqpfd.pdf

A CMOS MEMS thermal sensor with high frequency output

A low-power monolithic three-axis accelerometer with automatically sensor offset compensated and interface circuit

This study presents a simple approach to design and implement a solid-state micro tactile force sensor using the standard CMOS process (Fig. 1). By using the inductive sensing mechanism with the magnetic force contact interface and the CMOS on-chip analog circuit, the normal force is detected by the inductance change of the sensing coil and readout by characterizing the frequency variation of the LC tank oscillator. The proposed micro tactile force sensor has two major merits: (1) the fabrication process of the proposed tactile sensor is straightforward, and the fragile suspended structure is not required to detect the tactile load. Therefore, the process issues and the design concerns of the unwanted deformation induced by the residual stress of the CMOS thin films can be avoided. (2) Taking the advantages of the standard CMOS process (TSMC 1P6M CMOS process), the sensing component and the processing circuitry are monolithically integrated for direct signal processing with a better signal-to-noise ratio (SNR). The measurement results verify the feasibility and functionality of the proposed micro tactile sensor. For future perspectives, the proposed device can be exploited to the applications required compact tactile force sensing system. Moreover, more processing circuit components can be incorporated monolithically to provide more versatilities.

Sheng-Hsiang Tseng

Papers

Digital Offset Trimming Techniques for CMOS MEMS Accelerometers

A CMOS MEMS thermal sensor with high frequency output

A low-power monolithic three-axis accelerometer with automatically sensor offset compensated and interface circuit

CMOS Chip for Solid-State Tactile Force Sensor

A Low-Power Low-Noise Monolithic Accelerometer with Automatic Sensor Offset Calibration