Piezoelectric isolating transformer

1 . A piezoelectric isolating transformer characterized by an operating frequency range, the piezoelectric isolating transformer comprising a resonant structure having at least one mechanical resonance in the operating frequency range, said resonant structure comprising:

an insulating substrate having a first major surface and a second major surface opposite said first major surface; and

a first electro-acoustic transducer and a second electro-acoustic transducer mechanically coupled to said first major surface and said second major surface, respectively, of said substrate, one of said electro-acoustic transducers operable to convert an input electrical power in said operating frequency range to acoustic energy that excites mechanical vibration in said resonant structure, the other of said electro-acoustic transducers converting said mechanical vibration to output electrical power.

2 . The isolating transformer of claim 1 , in which said first electro-acoustic transducer comprises a thin-film electro-acoustic transducer.

3 . The isolating transformer of claim 1 , in which said first electro-acoustic transducer comprises a bottom electrode, a top electrode and a piezoelectric layer between said electrodes.

4 . The isolating transformer of claim 1 , in which:

said insulating substrate comprises a first substrate and a second substrate;

said first electro-acoustic transducer is located on said first substrate;

said second electro-acoustic transducer is located on said second substrate; and

said first substrate and said second substrate are bonded together with said first electro-acoustic transducer opposite said second electro-acoustic transducer.

5 . The isolating transformer of claim 1 , in which:

said isolating transformer additionally comprises an additional substrate bonded to said insulating substrate, said additional substrate defining a cavity; and

said first electro-acoustic transducer is located within said cavity.

6 . The isolating transformer of claim 5 , in which said piezoelectric isolating transformer additionally comprises a via extending through said insulating substrate and electrically connected to said first electro-acoustic transducer.

7 . The isolating transformer of claim 6 , additionally comprising contact pads outside said cavity, said contact pads electrically connected by said via to said first electro-acoustic transducer.

8 . The isolating transformer of claim 1 , in which said output electrical power and said input electrical power are characterized by respective voltages having a ratio dependent on a relationship between the frequency of said input electrical power and the frequency of said at least one mechanical resonance.

9 . A DC-to-DC converter, comprising:

an oscillator;

a rectifier; and

a piezoelectric isolating transformer comprising an input electrically connected to said oscillator, and an output electrically connected to said rectifier.

10 . The DC-to-DC converter of claim 9 , in which:

said piezoelectric isolating transformer is characterized by an operating frequency range and comprises a resonant structure having at least one mechanical resonance in said operating frequency range;

said oscillator generates input electrical power at a frequency in said operating frequency range; and

said resonant structure comprises:

an insulating substrate having a first major surface and a second major surface opposite said first major surface;

a first electro-acoustic transducer electrically connected to said input and mechanically coupled to said first major surface of said substrate, said first transducer converting said input electrical power to acoustic energy that excites mechanical vibration in said resonant structure; and

a second electro-acoustic transducer electrically connected to said rectifier and mechanically coupled to said second major surface of said substrate opposite said first electro-acoustic transducer, said second electro-acoustic transducer converting said mechanical vibration to output electrical power for rectification by said rectifier.

11 . The DC-to-DC converter of claim 10 , in which said first electro-acoustic transducer comprises a thin-film transducer.

12 . The DC-to-DC converter of claim 10 , in which said electro-acoustic first transducer comprises a bottom electrode, a top electrode, and a piezoelectric layer between said electrodes.

13 . The DC-to-DC converter of claim 9 , in which:

said piezoelectric isolating transformer additionally comprises an additional substrate bonded to said insulating substrate, said additional substrate defining a cavity; and

said first electro-acoustic transducer is located within said cavity.

14 . The DC-to-DC converter of claim 9 , in which said rectifier comprises a bridge rectifier.

15 . The DC-to-DC converter of claim 9 , in which:

said oscillator comprises a frequency control input; and

the DC-to-DC converter additionally comprises a feedback loop connected between said rectifier and said frequency control input of said oscillator, said feedback loop comprising an additional piezoelectric isolating transformer.

16 . The DC-to-DC converter of claim 15 , in which:

said additional piezoelectric isolating transformer comprises an input and an output; and

said feedback loop comprises:

a modulator electrically connected to receive a DC signal from said rectifier and an AC carrier signal from said output of said piezoelectric isolating transformer, said modulator having an output electrically connected to said input of said additional piezoelectric isolating transformer, and

a demodulator electrically connected to said output of said additional piezoelectric isolating transformer, said demodulator having an output, and

a comparator having inputs connected to a reference and said output of said demodulator and additionally having an output connected to said frequency control input of said oscillator.

17 . The DC-to-DC converter of claim 16 , in which:

said additional piezoelectric isolating transformer has a forward transmission coefficient dependent on the frequency of said AC carrier signal; and

said modulator modulates said AC carrier signal in response to said DC signal to generate a modulated carrier signal having modulation properties independent of said forward transmission coefficient of said additional piezoelectric isolating transformer.

18 . The DC-to-DC converter of claim 15 , additionally comprising a substrate common to said piezoelectric isolating transformer and said additional piezoelectric isolating transformer.

19 . The DC-to-DC converter of claim 15 , in which:

said second electro-acoustic transducer comprises a first sub-transducer and a second sub-transducer electrically connected in series to provide anti-phase voltages.

20 . A fabrication method, comprising:

providing an insulating substrate having a first major surface and a second major surface opposite said first major surface;

forming a first electro-acoustic transducer on said first major surface of said substrate; and

forming a second electro-acoustic transducer on said second major surface of said substrate opposite said first electro-acoustic transducer.

21 . The method of claim 20 , in which said first electro-acoustic transducer comprises a thin-film electro-acoustic transducer.

22 . The method of claim 20 , in which said insulating substrate comprises:

an at least partially-conducting substrate; and

a layer of insulating material between said first and second transducers.

23 . The method of claim 20 , in which:

said method additionally comprises providing a first substrate and a second substrate each having a first major surface and a second major surface opposite said first major surface;

said forming said first electro-acoustic transducer comprises forming said first electro-acoustic transducer on said first major surface of said first substrate;

said forming said second electro-acoustic transducer comprises forming said second electro-acoustic transducer on said first major surface of said second substrate; and

said providing said insulating substrate comprises joining said second major surface of said first substrate and said second major surface of said second substrate with said first electro-acoustic transducer opposite said second electro-acoustic transducer.

24 . The method of claim 20 , in which:

the method additionally comprises:

providing an additional substrate having a first major surface and a second major surface opposite said first major surface,

forming in said additional substrate a cavity extending into said additional substrate from said first major surface thereof, and

bonding said first major surface of said insulating substrate and said first major surface of said additional substrate with said first transducer located within said cavity; and

said forming said second electro-acoustic transducer comprises forming, after said bonding, said second electro-acoustic transducer on said second major surface of said insulating substrate opposite said first electro-acoustic transducer.

25 . The method of claim 24 , in which

the method additionally comprises:

forming in said insulating substrate a contact via extending from said first major surface of said insulating substrate, and

fabricating contact pads in contact with said contact via; and

said forming said first electro-acoustic transducer comprises forming said first electro-acoustic transducer on said first major surface of said insulating substrate electrically connected to said contact via.

26 . The method of claim 25 , additionally comprising removing substrate material from said second major surface of said insulating substrate to expose said contact via at said second major surface of said insulating substrate.