MEMS capacitive pressure sensor monolithically integrated with CMOS readout circuit by using post CMOS processes
© The Author(s) 2017
Received: 23 November 2016
Accepted: 28 December 2016
Published: 9 January 2017
In this paper, we presents a MEMS pressure sensor integrated with a readout circuit on a chip for an on-chip signal processing. The capacitive pressure sensor is formed on a CMOS chip by using a post-CMOS MEMS processes. The proposed device consists of a sensing capacitor that is square in shape, a reference capacitor and a readout circuitry based on a switched-capacitor scheme to detect capacitance change at various environmental pressures. The readout circuit was implemented by using a commercial 0.35 μm CMOS process with 2 polysilicon and 4 metal layers. Then, the pressure sensor was formed by wet etching of metal 2 layer through via hole structures. Experimental results show that the MEMS pressure sensor has a sensitivity of 11 mV/100 kPa at the pressure range of 100–400 kPa.
As the technologies of micro electromechanical systems (MEMS), micromachining, and nano-processes have been advanced, it becomes more important to accurately control and process the noisy signal from the MEMS-based precise sensors, improve the performance, reduce cost, and finally realize the system-on-chip concept . These benefits could be obtained by the monolithic integration of MEMS sensors with electronics, which has been applied to commercially available products such as accelerometers, bolometers, digital mirror displays, and so on [2–5].
The fabrication of MEMS structures using standard complementary metal oxide semiconductor (CMOS) device with minimal post processes has been exploited for several years, enabling the monolithic integration of MEMS structures and signal processing circuitry with just a few further steps after the CMOS process [6, 7]. To date, various CMOS–MEMS devices have been implemented by using post-CMOS process such as inertial sensors, magnetometers and pressure sensors, etc. [8–11].
The capacitive MEMS pressure sensors are one of the most widely used transducers of the various types of MEMS pressure sensors since they offer excellent noise performance, low power consumption, and easy integration with processing circuitry [9, 10, 12]. Narducci et al. reported a capacitive pressure sensor using aluminum metal layers of a commercial CMOS process as sensing electrodes . Cheng et al. improved the sensitivity by using multiple metal layers to form mechanical structure of a CMOS-based pressure sensor .
In this paper, we present the fabrication of a capacitive pressure sensor based on post-CMOS process and its characterization by using monolithically integrated circuitry.
The mechanical properties of the materials composing diaphragm
Young’s modulus (GPa)
The readout circuit for the proposed capacitive pressure sensor is based on a switched-capacitor scheme employing reference capacitors and sensing capacitors. We used fully differential scheme to suppress a signal drift by temperature variation and an error caused by the capacitance mismatch between reference and sensing capacitors.
Results and discussions
In this paper, we reported the fabrication of capacitive pressure sensor using post-CMOS process and measured its response at various applied pressures. The capacitive sensor was monolithically integrated with the CMOS circuitry processed by 0.35 μm foundry process to minimize the parasitic capacitance and electromagnetic interference noise. The readout circuit of fully differential structure based on switched-capacitor scheme was used to monitor the change of the sensing capacitor. The sensitivity of the fabricated sensor was 11 mV/100 kPa in the operation range of 100 to 400 kPa. As a future work, the integration of analog to digital converter and signal mining stage is required to improve the sensitivity and noise performance.
MJ participated in design, fabrication, and test the device and drafted the manuscript. KSY conceived of the study, reviewed all test methods and results, and finalized the drafted manuscript. Both authors read and approved the final manuscript.
The authors declare that they have no competing interests.
This research was supported by the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2016-H8501-16-1010) supervised by the IITP (Institute for Information & communications Technology Promotion), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2016R1A2B4014629), and IDEC (IC Design Education Center).
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