A novel sensor cell architecture and sensing circuit scheme for capacitive fingerprint sensors

Morimura, Hiroki; Shigematsu, Satoshi; Machida, Katsuyuki

doi:10.1109/4.841500

Cited by 55 publications

(30 citation statements)

References 3 publications

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“…The calculated Q factor of the fabricated pMUT transducer was about 198, which was higher than the Q factor of 111 in Ref. 4. Thus, our pMUT transducer presented much better launching performance than the previous work.…”

Section: Characterizationmentioning

confidence: 58%

“…1 The capacitive fingerprint sensors are the most widely used in consumer electronics, duo to their high array density and complementary metal-oxide-semiconductor transistor (CMOS) compatibility. [2][3][4] However, the image captured by capacitive fingerprint sensor is two-dimensional, which can be spoofed easily by a printed template. And capacitive fingerprint sensors are extremely sensitive to contamination and moisture on the finger, which may lead to false recognition.…”

mentioning

confidence: 99%

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Large-Scale and High-Density pMUT Array Based on Isolated Sol-Gel PZT Membranes for Fingerprint Imaging

Chen

et al. 2017

J. Electrochem. Soc.

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In this work, we proposed a novel ultrasonic transducer array based on an array of 50 × 50 piezoelectric micromachined ultrasonic transducers (pMUTs). The structure was specially designed for fingerprint imaging application. The pMUTs array were fabricated with isolated piezoelectric lead zirconate titanate (PZT) cells to reduce the crosstalk between adjacent units, and released by deepsilicon etching from the back side. The cell size and pitch of pMUTs were 50 μm and 100 μm, respectively. Layer-by-layer annealing method was used instead of one-time annealing during the fabrication of sol-gel based PZT film. The resonance frequency of the pMUT was about 24.82 MHz which agreed well with simulated 25.02 MHz. Besides, the effective electro-mechanical coupling coefficient (k eff ) and mechanical quality factor (Q factor) of the transducer were 0.1293 and 198, respectively. The equivalent circuit of the transducer was established and analyzed. The fitted admittance circle agreed well with the experimental result. This demonstration of pMUTs array has profound potential for large-scale, high-density, and high-frequency fingerprint imaging. Optical, capacitive, piezoelectric and acoustic mechanisms based sensors have been developed to capture the electronic images of human fingerprints in the last twenty years.1 The capacitive fingerprint sensors are the most widely used in consumer electronics, duo to their high array density and complementary metal-oxide-semiconductor transistor (CMOS) compatibility.2-4 However, the image captured by capacitive fingerprint sensor is two-dimensional, which can be spoofed easily by a printed template. And capacitive fingerprint sensors are extremely sensitive to contamination and moisture on the finger, which may lead to false recognition. Ultrasonic transducer array provides a potential solution to these problems. The acoustic impedances of valleys and ridges on fingerprints are greatly different, and can be easily distinguished by ultrasonic transducer.5 Thus, the ultrasonic pulse-echo imaging technology can be applied to imaging the ridges, valleys of the fingerprints, and even the tissue beneath. The three-dimensional images captured by ultrasonic fingerprint sensor eliminates the risks of failure and spoof.6 Large-scale, high-density pMUTs array based on AlN were used in high resolution fingerprint imaging with small size, high frame-rate and low cost. 7,8 The lead zirconate titanate (PZT) has piezoelectric coefficient that is generally two-orders-of-magnitude higher than AlN, 9-11 which can be used to fabricate fingerprint sensor with better performance. A PZT based fingerprint sensor was reported with single-pixel and mechanicalscanning working mode, which was large size, low frame-rate, and high cost. 12In this report, we demonstrate an ultrasound transducers array for fingerprint imaging based on sol-gel PZT technique. We designed the structures and parameters of the transducer by simulation, and fabricated the arrays of pMUTs based on the sol-gel PZT techniques. 13 The isolat...

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Section: Characterizationmentioning

confidence: 58%

mentioning

confidence: 99%

Large-Scale and High-Density pMUT Array Based on Isolated Sol-Gel PZT Membranes for Fingerprint Imaging

Chen

et al. 2017

J. Electrochem. Soc.

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show abstract

“…These include successive approximation [22], a relation oscillator [23][24], an RC-delay technique [25] and a charge transfer approach [26].…”

Section: Literature Review Capacitive Touch-screen Sensorsmentioning

confidence: 99%

Electrostatic Simulation Methodology for Capacitive Touch-Screen Panels

Cannon¹,

Brennan²

2014

25th IET Irish Signals &Amp; Systems Conference 2014 and 2014 China-Ireland International Conference on Information and Communi

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“…17.9. [66][67][68][69][70] In this circuit, the output voltage at the end of clock phase Φ 2 is given by (5) where C 1s is the sensor and C 1r is a reference capacitor equal to the sensor but not sensitive to the quantity to be measured. By choosing suitable values for C 2 , V sen , and V ref , it is possible to detect capacitance variations on the order of tens of attofarads (1 aF = 10 -18 F).…”

Section: Impedance Variationmentioning

confidence: 99%