Biometric authentication systems are used for authenticating users of devices incorporating the authentication systems. Biometric sensing technology provides a reliable, non-intrusive way to verify individual identity for authentication purposes.
Fingerprints, like certain other biometric characteristics, are based on unalterable personal characteristics and thus are a reliable mechanism to recognize individuals. There are many potential applications for utilization of biometric and fingerprint sensors. For example, fingerprint sensors may be used to provide access control in stationary applications, such as security checkpoints. Fingerprint sensors may also be used to provide access control in portable applications, such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, data storage devices, and the like. Accordingly, some applications, in particular portable applications, may require electronic fingerprint sensing systems that are compact, highly reliable, and inexpensive.
The higher the resolution of the biometric authentication system, the more detailed information it can obtain from the user. For example, a higher resolution fingerprint sensor obtains more detailed information from a user's fingerprint than a lower resolution fingerprint sensor. Higher detail fingerprint information allows for a more reliable mechanism to recognize individuals.
Many biometric sensors are capacitive. However, capacitive sensors have difficulty achieving resolutions higher than about 500 pixels per inch. Additionally, capacitive sensors have difficulty sensing through thick layers of material, as increasing the distance from the capacitive sensing elements tends to decrease signal strength and increase blurring between individual pixels. A higher resolution sensor that can more efficiently sense through thick layers of material is desired.