Silicon micromachined tactile imagers for use in live-scan fingerprinting and credit card applications

Credit cards are currently used extensively for financial transactions all across the globe. As an increasing number of financial transactions are implemented using credit cards and other card-access systems, it is important that mechanisms exist to improve their reliability and prevent the fraudulent use of these cards. Inkless electronic fingerprint readers can, in principle, be utilized to verify the identity of an individual using a credit card at point-of-sale terminals worldwide. This thesis describes the development of a low-cost silicon tactile imager for reading embossed characters on credit cards as an alternative when the magnetic strip on the card has failed. It also describes the development of high density silicon tactile imagers for live-scan fingerprinting. In addition to their use in financial transactions, electronic fingerprint scanners are very important to criminal justice agencies such as the FBI, as well as in electronic security systems and smart cards.; A high-compliance piezoresistive linear tactile array has been developed for reading embossed characters on credit cards. The sensor has 16 flexible silicon shanks and each shank is 6mm long, 100{dollar}mu{dollar}m wide and 10{dollar}mu{dollar}m thick. Polysilicon strain gauges incorporated on the shanks give a high-sensitivity analog readout as the tips of the shanks deflect over characters on the scanned surface. Fabrication is accomplished using a five-mask single-sided bulk-micromachined dissolved wafer process. The devices have a sensitivity of 10mV/mm at 5V and a minimum vertical resolution of l{dollar}mu{dollar}m.; High density planar capacitive tactile imagers have also been implemented for use in live-scan fingerprinting. Prototype 16 x 16-element arrays have been fabricated with both 300dpi and 500dpi spatial resolution. Each pixel is formed by the intersection of metal column lines on glass and {dollar}psp+{dollar} silicon row electrodes that are suspended by dual angular beams. Fabrication is achieved using a simple 7-mask dissolved-wafer process. The 300dpi and 500dpi arrays have force sensitivities of 150N/m and 90N/m, respectively; this can be easily adjusted by varying the beam thickness and is suitable for live-scan fingerprinting.