手机安全又有新玩法，超声波指纹传感器来了

"Our chip is fabricated from two wafers -- a MEMS wafer that contains the ultrasound transducers and a CMOS wafer that contains the signal processing circuitry," explained Horsley. "These wafers are bonded together, then the MEMS wafer is 'thinned' to expose the ultrasound transducers." (CMOS, or complementary metal-oxide-semiconductor, is the silicon-based technology used to make transistors in microchips.)

Horsley's group views ultrasound as the next frontier for MEMS technology. "Because we were able to use low-cost, high-volume manufacturing processes that produce hundreds of millions of MEMS sensors for consumer electronics each year, our ultrasound chips can be manufactured at an extremely low cost," he said.

The imager is powered by a 1.8-Volt power supply, using a power-efficient charge pump on their ASIC or application-specific integrated circuit. "Our ultrasound transducers have high sensitivity and the receiver electronics are located directly beneath the array, which results in low electrical parasitics," Horsley noted. "Using low-voltage integrated circuits will reduce the cost of our sensor and open up myriad new applications where the cost, size, and power consumption of existing ultrasound sensors are currently prohibitive."

Within the realm of biometrics and information security, the group's work is particularly significant, Horsley said. "Our ultrasonic fingerprint sensors have the ability to measure a three-dimensional, volumetric image of the finger surface and the tissues beneath the surface -- making fingerprint sensors more robust and secure."

Beyond biometrics and information security purposes, the new technology is expected to find many other applications, including "low-cost ultrasound as a medical diagnostic tool or for personal health monitoring," he added..

The group also made arrays of MEMS ultrasound devices with highly uniform characteristics, which allowed them to verify that the PMUTs have very similar frequency response characteristics.