Anodically bonded vacuum-sealed capacitive micromachined ultrasonic transducer (CMUT)
A capacitive micromachined ultrasonic transducer (CMUT) and methods of forming the same are disclosed herein. In one implementation, the CMUT comprises a glass substrate having a cavity; a patterned metal bottom electrode situated within the cavity of the glass substrate; and a vibrating plate comprising at least a conducting layer, wherein the vibrating plate is anodically bonded to the glass substrate to form an air-tight seal between the vibrating plate and the substrate and wherein a pressure inside the cavity is less than atmospheric pressure (i.e., a vacuum). In another implementation, the CMUT comprises a glass substrate with Through-Glass-Via (TGV) interconnects, wherein a metal electrode is electrically connected to a TGV and wherein said metal electrode can be in the bottom of a cavity of the glass substrate or on the vibrating plate.
1. A capacitive micromachined ultrasonic transducer (CMUT) comprising:
a glass substrate having a cavity, wherein the glass substrate has an inner edge defined by the cavity and an outer edge;
a patterned metal bottom electrode situated within the cavity of the glass substrate; and
a vibrating plate comprising at least a conducting layer and an insulating layer situated between the patterned metal bottom electrode and the conducting layer of the vibrating plate, wherein the insulating layer of the vibrating plate extends beyond the inner edge of the glass substrate and is anodically bonded to the glass substrate to form an air-tight seal between the vibrating plate and the glass substrate and wherein a pressure inside the cavity is less than atmospheric pressure.
2. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the insulating layer of the vibrating plate is attached to the bottom of the conducting layer of the vibrating plate.
3. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , further comprising an insulating layer on top of the patterned metal bottom electrode.
4. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the vibrating plate further comprises a metal electrode.
5. The capacitive micromachined ultrasonic transducer (CMUT) of claim 4 , wherein the vibrating plate metal electrode is situated on top of the conducting layer.
6. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the conducting layer of the vibrating plate comprises silicon.
7. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the insulating layer of the vibrating plate comprises silicon nitride.
8. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the glass substrate has a plurality of vacuum-sealed cavities, each cavity having a patterned metal bottom electrode.
9. The capacitive micromachined ultrasonic transducer (CMUT) of claim 8 , wherein the patterned metal bottom electrodes of the plurality of vacuum-sealed cavities are electrically connected to one another.
10. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , further comprising one or more conductive vias through the glass substrate, wherein the one or more through glass vias are used to electrically connect with at least one of the patterned bottom electrode, the conductive layer of the vibrating plate, or a metal electrode of the vibrating plate.
11. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the glass substrate comprises a borosilicate glass substrate.
12. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein a roughness of at least one of the glass substrate or the vibrating plate is greater than 0.5 nm.
13. The capacitive micromachined ultrasonic transducer (CMUT) of claim 1 , wherein the CMUT is operated in a conventional, collapse-snapback mode or a collapse mode.