Capacitive micromachined ultrasound transducer fabricated with epitaxial silicon membrane

• US 20060170014A1
• Filed: 03/30/2006
• Published: 08/03/2006
• Est. Priority Date: 12/27/2004
• Status: Active Grant

• Current Assignee: David Martin Mills, Jeffrey Bernard Fortin, John Robert Logan, Lowell Scott Smith, Wei-Cheng Tian
• Original Assignee: David Martin Mills, Jeffrey Bernard Fortin, John Robert Logan, Lowell Scott Smith, Wei-Cheng Tian
• Inventors: Mills, David Martin, Tian, Wei-Cheng, Smith, Lowell Scott, Fortin, Jeffrey Bernard, Logan, John Robert
• Granted Patent: US 7,545,012 B2
• Time in Patent Office: Days
• US Class Current: 257/252
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type

Abstract

A capacitive micromachined ultrasound transducer (cMUT) cell is presented. The cMUT cell includes a lower electrode. Furthermore, the cMUT cell includes a diaphragm disposed adjacent to the lower electrode such that a gap having a first gap width is formed between the diaphragm and the lower electrode, wherein the diaphragm comprises one of a first epitaxial layer or a first polysilicon layer. In addition, a stress reducing material is disposed in the first epitaxial layer.

Claims

1. A capacitive micromachined ultrasound transducer cell comprising:

a lower electrode;

a diaphragm disposed adjacent to the lower electrode such that a gap having a first gap width is formed between the diaphragm and the lower electrode, wherein the diaphragm comprises one of a first epitaxial layer or a first polysilicon layer; and

a stress reducing material disposed in one of the first epitaxial layer or the first polysilicon layer.

2. The capacitive micromachined ultrasound transducer cell of claim 1, wherein the stress reducing material comprises germanium.

3. The capacitive micromachined ultrasound transducer cell of claim 1, further comprising an upper electrode coupled to the diaphragm.

4. The capacitive micromachined ultrasound transducer cell of claim 1, wherein the diaphragm comprises the upper electrode.

5. The capacitive micromachined ultrasound transducer cell of claim 1, further comprising a material disposed on the diaphragm, wherein the material is configured for use as an upper electrode.

6. The capacitive micromachined ultrasound transducer cell of claim 5, wherein the material comprises one of a metal, a doped polysilicon, a doped epitaxial layer or any electrical conductive semiconductor material.

7. The capacitive micromachined ultrasound transducer cell of claim 1, further comprising a material disposed between the diaphragm and a second epitaxial layer in a configuration where the diaphragm and the second epitaxial layer are positioned opposite one another, and wherein the configuration is configured for use as the upper electrode.

8. A capacitive micromachined ultrasound transducer cell comprising:

a substrate; and

a diaphragm disposed on a first substrate, wherein one of the diagram or the first substrate are oppositely doped, and wherein a level of doping in the diaphragm is different than a level of doping in the first substrate.

9. The capacitive micromachined ultrasound transducer cell of claim 8, further comprising a stress reducing material disposed in the diaphragm.

10. The capacitive micromachined ultrasound transducer cell of claim 9, wherein the stress reducing material comprises germanium.

11. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the diaphragm comprises either a first epitaxial layer or a first polysilicon layer

12. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the diaphragm comprises an n-type material and the first substrate comprises a p-type material.

13. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the doping level of the diaphragm is high and the doping level of the first substrate is low.

14. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the doping level of the diaphragm is low and the doping level of the first substrate is high.

15. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the doping level of the diaphragm is in a range from about 1 e¹³ per cm³ to about 1 e²⁰ per cm³.

16. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the doping level of the substrate is in a range from about 1 e¹³ per cm³ to about 1 e²⁰ per cm³.

17. The capacitive micromachined ultrasound transducer cell of claim 8, wherein the diaphragm comprises a single crystal epitaxial layer.

18. A capacitive micromachined ultrasound transducer cell comprising:

a substrate;

a cavity formed in a topside of the substrate, wherein the cavity is defined by a plurality of support posts;

a lower electrode disposed at a bottom of the cavity;

a diaphragm disposed on the plurality of support posts to form a composite structure having a gap between the lower electrode and the diaphragm; and

a stress reducing material disposed in the diaphragm.

19. The capacitive micromachined ultrasound transducer cell of claim 18, wherein the diaphragm comprises one of a first epitaxial layer or a first polysilicon layer.

20. The capacitive micromachined ultrasound transducer cell of claim 18, wherein the diaphragm and the substrate are oppositely doped, and wherein a doping level in the diaphragm is different than a doping level in the substrate.