MEMS fingerprint sensor immune to various finger surface conditions

Abstract

This paper describes a new fingerprint sensor that detects the topography of finger ridges and valleys. We propose a microelectromechanical systems (MEMS) cavity structure for the pixels arrayed on the sensor surface and a fabrication process that stacks the cavity structures on a CMOS LSI. A thin film on top of the cavity structures is bent by finger ridges mechanically, which is detected by the sensing circuits below them electronically. Based on an analytical model, we designed a cavity structure suitable for fingerprint detection. We fabricated the cavity structures on the sensing circuits by a fabrication process that entails gold electroplating, sacrificial layer etching for cavities, and a sealing technique. The fabricated fingerprint sensor consists of about 57 334 pixels in the area of 11.2 mm 12.8 mm, which yields a high spatial resolution of 508 dots-per-inch (dpi). With these pixels working together, fingerprint images were obtained. The sensor produces clear fingerprint images regardless whether the finger was dry or wet, which confirms its potential for various practical applications.Index Terms-Fingerprint image, fingerprint sensor, LSI, microelectromechanical systems, process.

Three-Dimensional Silicon Smart Tactile Imager Using Large Deformation of Swollen Diaphragm with Integrated Piezoresistor Pixel Circuits

“…Also, the integration density of organic-FET is much lower than the present silicon technology, and its long term reliability in force sensor applications has not yet been demonstrated. Silicon-MEMS tactile imagers, integrating micro pressure sensor array (Sugiyama et al, 1990) or micro force-sensor array, have been reported earlier ; (b); Kobayashi et al, 1990;Souza & Wise, 1997;Mei et al, 1999;Mei et al, 2000;Sato et al, 2003;Charlot et al, 2004). This type of sensors can reduce the number of electronic signal wires by integrated switching matrix fabricated using CMOS technology (Doelle et al, 2004).…”

Analysis and design of a wide micro beam as a pressure gauge for high sensitivity MEMS fingerprint sensors

“…MEMS devices have been the recent interest in fingerprint acquisition systems such as the works done by Souza and Wise 1997;Charlot et al 2004;Takao et al 2004;Knapp 2004;Fojimori et al 2005;Sato et al 2003Sato et al , 2004Sato et al , 2005. MEMS Capacitive fingerprint sensors offer many advantages over existing technologies for biometrics extraction.…”

“…They are a promising alternative due to low power consumption, non bulky structures and no turn on temperature drifts. Recent prototypes have tried to fabricate the sensor on flexible substrate (Takao et al 2004), improve sensitivity (Sato et al 2004), make the device immune to finger surface condition (Sato et al 2003), make a single chip sensor (Fojimori et al 2005), or other modifications but most are not commercially manufactured which means there are still rooms for improvements on price and performance.…”

Tuning the sensing range and sensitivity of three axes tactile sensors using the polymer composite membrane

“…There are various fabrication processes have been exploited to implement the tactile sensors. For instance, the silicon-based process [1][2][3][4][5][6], such as the CMOS and bulk micromachining processes, and the nonsilicon-based process [7][8][9][10][11][12], such as the polymer process. As a result, the variety as well as the performance of the tactile sensor has been significantly improved by the fabrication processes.…”