Abstract
Capacitive Micromachined Ultrasonic Transducers (CMUTs) fabricated using Silicon-On-Insulator (SOI) wafers often have large thickness variation of the flexible plate, which causes variation in both pull-in voltage and resonant frequency across the CMUT array. This work presents a bond and boron etch-stop scheme for fabricating the flexible plate of a CMUT. The proposed fabrication method enables precise control of the plate thickness variation and is a low cost alternative to the SOI-based process. N-type silicon wafers are doped with boron to a surface concentration of > 1020 cm−3 using solid planar diffusion predeposition at 1125 °C for 30, 60, and 90 min. Process simulations are used to predict the boron doping profiles and validated with secondary ion mass spectrometry measurements. The doped wafers are fusion-bonded to a silicon dioxide surface and thinned down using an 80 °C, 20 wt% potassium hydroxide solution with isopropyl alcohol added to increase the etch selectivity to the highly doped boron layer. The resulting plate thickness uniformity is estimated from scanning electron micrographs to a mean value of 2.00μm±2.5%. The resonant frequency in air for a 1-D linear CMUT array is measured to 12MHz±2.5%. Furthermore, hydrophone measurements show that the fabricated devices can be used to emit sound pressure in the ultrasonic frequency domain.
Original language | English |
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Title of host publication | Proceedings of 2016 IEEE International Ultrasonics Symposium, 2016 |
Number of pages | 4 |
Publisher | IEEE |
Publication date | 2016 |
ISBN (Print) | 978-1-4673-9898-5 |
ISBN (Electronic) | 978-1-4673-9897-8 |
DOIs | |
Publication status | Published - 2016 |
Event | 2016 IEEE International Ultrasonics Symposium - Convention Center Vinci Tours, Tours, France Duration: 18 Sep 2016 → 21 Sep 2016 https://ieeexplore.ieee.org/xpl/conhome/7589760/proceeding |
Conference
Conference | 2016 IEEE International Ultrasonics Symposium |
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Location | Convention Center Vinci Tours |
Country/Territory | France |
City | Tours |
Period | 18/09/2016 → 21/09/2016 |
Internet address |