Integrated piezoelectric microelectromechanical ultrasound transducer (PMUT) on integrated circuit (IC) for fingerprint sensing
Microelectromechanical (MEMS) devices and associated methods are disclosed. Piezoelectric MEMS transducers (PMUTs) suitable for integration with complementary metal oxide semiconductor (CMOS) integrated circuit (IC), as well as PMUT arrays having high fill factor for fingerprint sensing, are described.
1. A method, comprising:
forming a plurality of cavities in a complementary metal oxide semiconductor (CMOS) device wafer, wherein the forming a plurality of cavities further comprises:
filling the plurality of cavities in the CMOS device wafer with sacrificial material;
planarizing the sacrificial material on the CMOS device wafer;
depositing a capping layer over the sacrificial material;
forming at least one opening in the capping layer to expose the sacrificial material;
selectively removing the sacrificial material; and
sealing the at least one opening in the capping layer;
depositing and patterning a piezoelectric layer comprising scandium over the plurality of cavities;
forming a plurality of openings in the piezoelectric layer to expose a first conductive material layer under the piezoelectric layer and to expose at least one CMOS device wafer electrode; and
depositing and patterning a second conductive material layer over and adjacent to the piezoelectric layer to establish an electrical connection between the at least one CMOS device wafer electrode and the second conductive material layer.
2. The method of claim 1 , wherein the forming the plurality of cavities comprises forming a piezoelectric MUT (PMUT) array of a fingerprint sensor adapted to sense a characteristic of a fingerprint placed adjacent to the PMUT array and opposite the plurality of cavities.
3. The method of claim 2 , wherein the forming the PMUT array comprises forming a plurality of PMUT devices in at least one of a rhombus configuration or a hexagonal configuration.
4. The method of claim 3 , wherein the forming the plurality of PMUT devices comprises forming a first two of the plurality of PMUT devices in the rhombus configuration and a second two of the plurality of PMUT devices in the hexagonal configuration arranged as a unit cell.
5. The method of claim 1 , further comprising:
depositing the first conductive material layer comprising a metal conductive layer over the capping layer.
6. The method of claim 1 , wherein the depositing and patterning the piezoelectric layer comprising scandium comprises depositing and patterning scandium doped aluminum nitride comprising about 20 percent (%) to about 30% scandium.
7. The method of claim 1 , wherein the forming the plurality of openings in the piezoelectric layer and the depositing and patterning the second conductive material layer over the piezoelectric layer comprises forming at least one bottom electrode electrically coupled to at least one top electrode via the piezoelectric layer.
8. The method of claim 7 , further comprising:
depositing an acoustic propagation layer over the at least one top electrode.
9. The method of claim 8 , further comprising:
depositing a cover layer over the acoustic propagation layer.
10. The method of claim 8 , wherein the depositing the acoustic propagation layer comprises depositing at least one of a liquid, a polymer, or an acoustic impedance matching material configured to provide acoustic impedance matching between a PMUT device associated with the at least one top electrode and the cover layer.