Parametrically Amplified Low-Power MEMS Capacitive Humidity Sensor

Abstract

We present the design, fabrication, and response of a polymer-based Laterally Amplified Chemo-Mechanical (LACM) humidity sensor based on mechanical leveraging and parametric amplification. The device consists of a sense cantilever asymmetrically patterned with a polymer and flanked by two stationary electrodes on the sides. When exposed to a humidity change, the polymer swells after absorbing the analyte and causes the central cantilever to bend laterally towards one side, causing a change in the measured capacitance. The device features an intrinsic gain due to parametric amplification resulting in an enhanced signal-to-noise ratio (SNR). 11-fold magnification in sensor response was observed via voltage biasing of the side electrodes without the use of conventional electronic amplifiers. The sensor showed a repeatable and recoverable capacitance change of 11% when exposed to a change in relative humidity from 25-85%. The dynamic characterization of the device also revealed a response time ~1s and demonstrated a competitive response with respect to a commercially available reference chip.

A Review of Actuation and Sensing Mechanisms in MEMS-Based Sensor Devices

“…The actuation technique is a term given to the mechanism that transforms the input energy into a microstructure motion. There are different principles and approaches to actuate MEMS devices [7,[50][51][52][53][54][55], the most important of which include: electrostatic actuation [56][57][58][59][60][61][62][63][64], electrothermal actuation [4,44,[65][66][67][68], electromagnetic actuation [7,69], and piezoelectric actuation [48,70] (Fig. 2).…”

“…biosensor application [56], humidity sensing [57], particle and mass sensing applications [50,78], MEMS nanopositioning system [58], RF MEMS switch applications [13,79], closed-loop noise of MEMS oscillators [60], navigation (automobile Global Positioning System GPS) [62,80], gyroscopes [81], biomarker detection in exhaled breath [82] and mass-sensitive gas sensors [63]. Besides, the theoretical model of electrostatically actuated and capacitive CMOS-MEMS based sensor device for noninvasive screening of diabetes was also reported.…”

“…The output signal of the device will be measured as a voltage due to change in the sensing capacitance upon (10) actuation using MS3110 capacitive readout circuit that translates the change in capacitance to the output voltage change in response to the temperature of the microheaters. Nowadays, capacitive effects are used in MEMS resonators [60], biosensor application [56], humidity sensor [57], diabetes screening [66], Navigation (automobile Global Positioning System (GPS)) [62], a low noise accelerometer [131], and RF MEMS capacitive switches [132].…”

A Capacitive MEMS Inclinometer Sensor with Wide Dynamic Range and Improved Sensitivity

“…MEMS capacitance sensors mainly consist of capacitor electrodes and insulation medium. The amount of capacitance is related to the distance and the area between two electrodes [ 13 , 14 ]. In the MEMS fabrication process, the capacitors can be easily fabricated by using sputtering or plating methods [ 15 ].…”