CMUT-on-CMOS ultrasonic transducer by bonding active wafers and manufacturing method thereof

A SOC (system-on-chip) ultrasonic transducer, comprising:

• a first chip, wherein the first chip comprises a silicon substrate and substrate material, wherein the silicon substrate includes prefabricated CMOS circuits and wherein the substrate material includes prefabricated a CMUT first electrode and at least two layers of metal interconnects;
• and
• a second chip, wherein the second chip includes prefabricated CMOS circuits, a cavity, and a CMUT second electrode,
• wherein the first chip or the second chip does not include SOI material,
• wherein the first chip and the second chip are face to face combined by fusion bonding,
• wherein the second chip comprises a thinned monocrystalline silicon layer which works as a mechanical layer of CMUT, and wherein the thinning comprises chemical etching the second wafer on the back side with a thinning uniformity requirement of +/−0.2 micrometers;
• the cavity and the CMUT second electrode have predetermined size parameters;
• the second chip comprises drain end of high voltage transistor or high/low voltage device isolation.