Fabrication of a Low-Frequency Ultrasonic Transducer

Inhalt:
An improved process for the fabrication of capacitive ultrasonic transducer is proposed. The transducer consists of a membrane carrier and a recessed substrate. It is assembled together through a newly developed direct bonding technology. Benefited from the separate component preparations, low frequency transducers of 100 to 500 kHz can be realized. Two major aims are realized in this investigation. First, both top and bottom electrodes are arranged on the same side of the device. Therefore, no vertical via is required to address the bottom electrode. Second, a self-stop etching scheme is proposed and successfully implemented, which leads to regular and uniform recesses of 2 to 7 microns depth. Initial tests validate the effectiveness of these improvements. This transducer can be used for airborne and immersion applications.