US 12,226,799 B2
Method of manufacturing capacitive micromachined ultrasonic transducer (CMUT)
Nicolas Senegond, Tours (FR); Dominique Gross, Tours (FR); and Cyril Meynier, Tours (FR)
Assigned to VERMON SA, Tours (FR)
Appl. No. 17/630,059
Filed by VERMON SA, Tours (FR)
PCT Filed Jul. 16, 2020, PCT No. PCT/IB2020/000617
§ 371(c)(1), (2) Date Jan. 25, 2022,
PCT Pub. No. WO2021/019296, PCT Pub. Date Feb. 4, 2021.
Claims priority of provisional application 62/879,056, filed on Jul. 26, 2019.
Prior Publication US 2022/0274133 A1, Sep. 1, 2022
Int. Cl. H01G 7/00 (2006.01); B06B 1/02 (2006.01)
CPC B06B 1/0292 (2013.01) 8 Claims
OG exemplary drawing
 
1. A method of manufacturing a capacitive micromachined ultrasonic transducer (CMUT), comprising the steps of:
a) forming a first silicon oxide layer on a side of a surface of a first substrate;
b) forming a second silicon oxide layer on a side of a surface of a second substrate;
c) forming a cavity in the first silicon oxide layer or the second silicon oxide layer;
d) after steps a), b), and c), assembling a first structure formed in step a) comprising the first substrate and the first silicon oxide layer with a second structure formed in step b) comprising the second substrate and the second silicon oxide layer, by direct bonding of a surface of the second silicon oxide layer opposite to the second substrate to a surface of the first silicon oxide layer opposite to the first substrate;
e) after step d), removing the second substrate to only keep above the cavity a suspended membrane formed by the second silicon oxide layer; and
f) after step e), forming an upper electrode on a surface of the suspended membrane opposite to the first substrate,
wherein step f) comprises a step of deposition of a first metal layer on top of and in contact with the surface of the suspended membrane opposite to the first substrate, followed by a step of deposition of a second metal layer on top of and in contact with a surface of the first metal layer opposite to the suspended membrane, followed by a step of local removal of portions of the first metal layer and the second metal layer to localize the upper electrode opposite the cavity, wherein the first metal layer has a work function higher than a work function of the second metal layer, and wherein the first substrate is made of a doped semiconductor material and forms a lower electrode of the CMUT.