Low-frequency complementary metal oxide semiconductor (CMOS) ultrasonic transducer
In accordance with at least one example of the description, a device includes a substrate and a linear array of transducer elements across the substrate and forming a cavity region. The cavity region is bounded by a first termination region and a second termination region. The linear array of transducer elements includes a transducer element having a front-end-of-line (FEOL) portion that is formed by a FEOL process and a back-end-of-line (BEOL) portion that is formed by an n-layer BEOL process. The BEOL portion of the transducer element includes a ferroelectric capacitor and a conductive element. The conductive element is formed by metal layer-n of the n-layer BEOL process, where n denotes an integer greater than 3.
1 . A device, comprising:
a substrate; and
transducer elements over the substrate, each transducer element including a ferroelectric capacitor and a conductive element spaced from the ferroelectric capacitor by a dielectric material, the ferroelectric capacitor being between the conductive element and the substrate.
2 . The device of claim 1 , wherein:
the conductive element is a first conductive element;
the transducer element further includes a second conductive element between the first conductive element and the ferroelectric capacitor.
3 . The device of claim 2 , wherein the first conductive element is electrically isolated from an electrode of the ferroelectric capacitor.
4 . The device of claim 2 , wherein the first conductive element has a first width and the second conductive element has a second width that is equal to the first width.
5 . The device of claim 1 , further comprising:
a polysilicon layer between the substrate and the transducer elements, wherein the polysilicon layer is coupled to a ground terminal.
6 . The device of claim 5 , wherein the polysilicon layer is part of a front end of line (FEOL) structure.
7 . The device of claim 1 , wherein the ferroelectric capacitors of the transducer elements are first ferroelectric capacitors forming a cavity region, the device further comprising a first termination region including second ferroelectric capacitors and a second termination region including third ferroelectric capacitors, the first ferroelectric capacitors electrically coupled to an excitation source, and the second and third ferroelectric capacitors electrically isolated from the excitation source.
8 . The device of claim 7 , wherein the first termination region has a first acoustic impedance, and the cavity region has a second acoustic impedance that is different from the first acoustic impedance to form an acoustic impedance mismatch between the first termination region and the cavity region.
9 . The device of claim 7 , wherein the cavity region has an odd number of the transducer elements.
10 . The device of claim 7 , wherein the cavity region has an even number of the transducer elements.
11 . The device of claim 7 , wherein a wavelength of a surface acoustic wave inducible by exciting a resonance mode of the cavity region is λ; and neighboring transducer elements are spaced at a pitch of λ/2.
12 . The device of claim 1 , wherein the ferroelectric capacitor and the conductive element are in a metallization structure or a back end of line (BEOL) structure over the substrate.
13 . The device of claim 1 , wherein the conductive element is a first conductive element, and the transducer element further comprises a second conductive element over and electrically isolated from the first conductive element.
14 . The device of claim 13 , wherein the second conductive element has a same width as the first conductive element.
15 . The device of claim 13 , wherein the second conductive element has a different width from the first conductive element.
16 . The device of claim 13 , wherein the first and second conductive element and the ferroelectric capacitor are part of a metallization structure or a BEOL structure.