Compliant micro device transfer head

1. A micro device transfer head comprising:

a base substrate;

a spring member including:

a spring anchor coupled to the base substrate; and

a spring portion comprising an electrode, wherein the spring portion is deflectable into a space between the spring portion and the base substrate;

a dielectric layer covering a top surface of the electrode; and

a sensor integrated with the spring member to measure an amount of deflection of the spring portion.

2. The micro device transfer head of claim 1 , wherein the spring portion further comprises a mesa structure protruding away from the base substrate.

3. The micro device transfer head of claim 2 , wherein the mesa structure is integrally formed with the spring portion.

4. The micro device transfer head of claim 2 , further comprising an electrode lead running from the electrode to the spring anchor of the spring member.

5. The micro device transfer head of claim 4 , wherein the electrode lead runs along a top surface of the spring member.

6. The micro device transfer head of claim 5 , wherein the dielectric layer covers the electrode lead along the top surface of the spring member.

7. The micro device transfer head of claim 4 , further comprising a via through the mesa structure connecting the electrode to the electrode lead.

8. The micro device transfer head of claim 1 , wherein the sensor comprises a material selected from a group consisting of a piezoelectric material and a piezoresistive material.

9. The micro device transfer head of claim 1 , wherein the sensor is coupled to the spring member.

10. The micro device transfer head of claim 1 , wherein the sensor is formed within the spring member.

11. The micro device transfer head of claim 1 , wherein the sensor comprises a first electrode on a bottom surface of the spring portion and a second electrode formed on the base substrate within the space and opposite the first electrode.

12. The micro device transfer head of claim 1 , wherein the sensor is selected from a group consisting of a capacitive sensor and a strain gauge.

13. The micro device transfer head of claim 2 , wherein the space is a cavity in the base substrate.

14. The micro device transfer head of claim 13 , wherein the spring member is a spring arm having a first end coupled to the base substrate and a second end suspended above the cavity, wherein the first end comprises the spring anchor and the second end comprises the spring portion.

15. The micro device transfer head of claim 13 , wherein the spring member completely covers the cavity.

16. The micro device transfer head of claim 15 , wherein the mesa structure is formed over a center of the cavity.

17. The micro device transfer head of claim 2 , further comprising a second electrode on the top surface of the mesa structure to form a pair of electrodes, wherein the dielectric layer covers the pair of electrodes.

18. The micro device transfer head of claim 1 , wherein the spring portion is elevated above the base substrate by the spring anchor.

19. The micro device transfer head of claim 18 , wherein the spring member is a spring arm.

20. The micro device transfer head of claim 1 , wherein the spring member comprises a plurality of spring arms.

21. A micro device transfer head array comprising:

an array of transfer heads, each comprising:

a base substrate;

a spring member including:

a spring anchor coupled to the base substrate; and

a spring portion comprising an electrode, wherein the spring portion is deflectable into a space between the spring portion and the base substrate;

a dielectric layer covering a top surface of the electrode; and

a sensor integrated with the spring member to measure an amount of deflection of the spring portion.

22. The micro device transfer head array of claim 21 , wherein the space of each transfer head is a cavity in the base substrate.

23. The micro device transfer head array of claim 22 , wherein the spring member is a spring arm having a first end coupled to the base substrate and a second end suspended above the cavity, wherein the first end comprises the spring anchor and the second end comprises the spring portion.

24. The micro device transfer head array of claim 22 , wherein the spring member completely covers the cavity.

25. The micro device transfer head array of claim 21 , wherein the sensor comprises a material selected from a group consisting of a piezoelectric material and a piezoresistive material.

26. A method of transferring an array of micro devices comprising:

depressing each transfer head in an array of transfer heads, each transfer head comprising:

a base substrate;

a spring member including:

a spring anchor coupled to the base substrate; and

a spring portion comprising an electrode, wherein the spring portion is deflectable into a space between the spring portion and the base substrate; and

a dielectric layer covering a top surface of the electrode;

applying a voltage to each transfer head to maintain the depressed position;

removing the voltage from a portion of the transfer heads to selectively release the portion of the transfer heads from the depressed position to form a selectively-released array of transfer heads;

positioning the selectively-released array of transfer heads over an array of micro devices;

contacting the array of micro devices with the selectively-released array of transfer heads;

picking up a portion of the array of micro devices corresponding to the released portion of transfer heads in the selectively-released array of transfer heads; and

releasing the portion of the array of micro devices onto at least one receiving substrate.

27. The method of claim 26 , wherein the transfer head further comprises:

a backside electrode on the bottom surface of the spring portion;

an opposing electrode on the base substrate within the space and opposite the backside electrode; and

a dielectric layer formed over the surface of the opposing electrode.