CRYSTAL OSCILLATORS AND METHODS FOR FABRICATING THE SAME

1 . A crystal oscillator, comprising

a convex crystal resonator having a first surface and a second surface, wherein the first surface comprises at least one convex-shaped portion and the second surface is substantially planar;

at least one pair of first electrodes disposed on the first surface; and

at least one second electrode disposed on the second surface.

2 . The crystal oscillator of claim 1 , wherein the at least one pair of first electrodes and the at least one second electrode comprise a conductive material.

3 . The crystal oscillator of claim 2 , wherein the conductive material comprises gold, platinum, titanium, chromium, aluminum, nickel, silver, or a combination thereof.

4 . The crystal oscillator of claim 1 , wherein the at least one pair of first electrodes and the at least one second electrode comprise gold.

5 . The crystal oscillator of claim 1 , wherein the convex crystal resonator comprises AT-cut crystal.

6 . (canceled)

7 . (canceled)

8 . The crystal oscillator of claim 1 ,

wherein the first surface of the convex crystal resonator comprises one convex-shaped portion, and wherein the at least one pair of first electrodes is aligned with the one convex-shaped portion.

9 . The crystal oscillator of claim 8 , wherein at least one second electrode is aligned with the one convex-shaped portion.

10 . The crystal oscillator of claim 1 , wherein the first surface of the convex crystal resonator comprises two or more convex-shaped portions, wherein the at least one pair of first electrodes includes a plurality of pairs of first electrodes, and wherein each of the two or more convex-shaped portions is aligned with a respective pair of first electrodes of plurality of pairs of first electrodes.

11 . The crystal oscillator of claim 10 , wherein the at least one second electrode includes a plurality of second electrodes wherein each of the two or more convex-shaped portions is aligned with a respective second electrode of the plurality of second electrodes.

12 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a thickness of less than about 1 mm.

13 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a thickness of less than about 0.5 mm.

14 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a thickness of about 0.1 mm.

15 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a fluctuation of oscillation frequency of less than about 0.1 ppm.

16 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a fluctuation of oscillation frequency of less than about 0.01 ppm.

17 . The crystal oscillator of claim 1 , wherein the crystal oscillator has a length of less than about 5 mm.

18 . The crystal oscillator of claim 17 , wherein the crystal oscillator has a width of less than about 5 mm.

19 . (canceled)

20 . A method to fabricate a crystal oscillator, the method comprising:

providing a crystal substrate;

forming at least one convex portion in the crystal substrate;

forming at least one pair of first electrodes on a first surface of the at least one convex portion of the crystal substrate; and

forming at least one second electrode on a second surface of the at least one convex portion of the crystal substrate.

21 . The method of claim 20 , wherein the first surface of the at least one convex portion includes a convex-shaped surface.

22 . The method of claim 21 , wherein the second surface of the at least one convex portion is substantially planar.

23 . The method of claim 20 , wherein forming the at least one convex portion in the crystal substrate comprises:

applying a photoresist on a surface of the crystal substrate;

patterning the photoresist on the surface of the crystal substrate to form a patterned photoresist;

curing the patterned photoresist; and

etching the crystal substrate and the patterned photoresist to form the at least one convex portion.

24 . The method of claim 23 , wherein forming the at least one convex portion further comprises determining a sectional profile of the at least one convex portion.

25 . The method of claim 23 , wherein applying the photoresist comprises applying a diazonaphthoquinone (DNQ).

26 . The method of claim 23 , wherein patterning the photoresist comprises patterning by exposure or heat.

27 . The method of claim 23 , wherein patterning the photoresist is based, at least in part, on sectional profile of the at least one convex portion.

28 . (canceled)

29 . The method of claim 23 , wherein applying the photoresist includes applying a positive photoresist.

30 . The method of claim 29 , wherein applying the photoresist includes applying a photoresist that comprises an optionally substituted diazonaphthoquinone (DNQ), or a mixture of DNQ and a phenol formaldehyde resin.

31 . The method of claim 23 , wherein etching includes etching the crystal substrate and the patterned photoresist via reactive ion etching.

32 . The method of claim 23 , wherein etching comprises etching the crystal substrate and the patterned photoresist at different etching rates.

33 . The method of claim 20 , wherein forming the at least one pair of first electrodes comprises:

depositing a conductive material on the first surface of the at least one convex portion; and

patterning the conductive material deposited on the first surface to form the at least one pair of first electrodes.

34 . The method of claim 20 , wherein forming the at least one second electrode comprises:

depositing a conductive material on the second surface of the at least one convex portion; and

patterning the conductive material deposited on the second surface to form the at least one second electrode.

35 . (canceled)

36 . The method of claim 33 , wherein depositing the conductive material comprises depositing gold, platinum, titanium, chromium, aluminum, nickel, silver, or a combination thereof.

37 . (canceled)

38 . (canceled)

39 . A sensor, comprising;

a crystal oscillator, comprising;

a convex crystal resonator having a first surface and a second surface, wherein the first surface comprises at least one convex-shaped portion and the second surface is substantially planar;

at least one pair of first electrodes disposed on the first surface;

at least one second electrode disposed on the second surface; and

a material disposed on the at least one second electrode, wherein the material is sensitive to an analyte.

40 . The sensor of claim 39 , wherein the material that is sensitive to the analyte has a selective affinity for the analyte.

41 . The sensor of claim 39 , wherein the analyte includes an odor or gas.

42 . The sensor of claim 41 , wherein the gas includes a combustible gas, a flammable gas, a toxic gas, or a combination thereof.

43 . The sensor of claim 41 , wherein the gas includes CO, CO 2 , CH 4 , O 2 , H 2 , NH 3 , C 2 H 5 OH, or a combination thereof.

44 . A method to detect an analyte, the method comprising:

providing a sample suspected to contain an analyte;

contacting a sensor with the sample, wherein the sensor comprises,

a crystal oscillator, comprising

a convex crystal resonator having a first surface and a second surface, wherein the first surface comprises at least one convex-shaped portion and the second surface is substantially planar;

at least one pair of first electrodes disposed on the first surface; and

at least one second electrode disposed on the second surface; and

a material disposed on the at least one second electrode, wherein the material is sensitive to the analyte; and

determining a change in resonance frequency of the convex crystal resonator.

45 . The method of claim 44 , wherein the sample includes a gas sample.

46 . The method of claim 44 , wherein the analyte includes an odor or gas.

47 . The method of claim 45 , wherein the gas sample comprises a combustible gas, a flammable gas, a toxic gas, or a combination thereof.