Method of forming an array of a multi-device unit cell
Backplane-side bonding structures including a common metal are formed on a backplane. Multiple source coupons are provided such that each source coupon includes a transfer substrate and an array of devices to be transferred. Each array of devices are arranged such that each array includes a unit cell structure including multiple devices of the same type and different types of bonding structures including different metals that provide different eutectic temperatures with the common metal. Different types of devices can be sequentially transferred to the backplane by sequentially applying the supply coupons and selecting devices providing progressively higher eutectic temperatures between respective bonding pads and the backplane-side bonding structures. Previously transferred devices stay on the backplane during subsequent transfer processes, enabling formation of arrays of different devices on the backplane.
1. A device assembly comprising a periodic array of multiple instances of a unit cell structure located on a backplane, wherein each instance of the unit cell structure comprises:
multiple bonded material portions located within an area of a respective instance of the unit cell structure, wherein each of the multiple bonded material portions is in direct contact with a top surface of the backplane and has a respective metallic bonding material composition which comprises a compound of a common element and a respective unique element that is not present in any other of the multiple bonded material portions;
a first device bonded to the backplane through a first bonded material portion of the multiple bonded material portions, the first bonded material portion containing a first metallic bonding material composition; and
a second device bonded to the backplane through a second bonded material portion of the multiple bonded material portions, the second bonded material portion containing a second metallic bonding material composition, wherein:
the first metallic bonding material composition and the second metallic bonding material composition include the common metal;
the first metallic bonding material composition includes the respective unique element comprising a first metal that is not present in the second metallic bonding material composition; and
the second metallic bonding material composition includes another respective unique element comprising a second metal that is not present in the first metallic bonding material composition.
2. The device assembly of claim 1 , wherein each instance of the unit cell structure further comprises a third device bonded to the backplane through a third bonded material portion of the multiple bonded material portions, the third bonded material portion containing a third metallic bonding material composition, wherein the third metallic bonding material composition includes the common metal, does not include the first metal or the second metal, and includes a third metal that is different from the common metal, the first metal, and the second metal.
3. The device assembly of claim 2 , wherein:
the first device is a first light emitting device that is configured to emit light with a peak intensity at a first wavelength;
the second device is a second light emitting device that is configured to emit light with a peak intensity at a second wavelength that is different from the first wavelength; and
the third device is a third light emitting device that is configured to emit light with a peak intensity at a third wavelength that is different from the first and second wavelengths.
4. The device assembly of claim 1 , wherein top surfaces of all instances of the first device and the second device are within a same horizontal plane.
5. The device assembly of claim 1 , wherein the periodic array is a two-dimensional rectangular periodic array in which the multiple instances of the unit cell structure are repeated in two orthogonal directions that are parallel to a surface of the backplane to which the periodic array is attached.
6. The device assembly of claim 3 , wherein:
the first light emitting device comprises a first light emitting diode which is configured to emit light of a first color;
the second light emitting device comprises a second light emitting diode which is configured to emit light of a second color that is different from the first color;
the third light emitting device comprises a third light emitting diode which is configured to emit light of a third color that is different from the first and second colors; and
the device assembly comprises an emissive display panel which contains the first, second and third light emitting diodes.
7. The device assembly of claim 6 , wherein:
the emissive display panel comprises a direct view display panel;
the first color comprises a red color;
the second color comprises a green color; and
the third color comprises a blue color.
8. The device assembly of claim 6 , further comprising sensors which are bonded to the backplane.
9. The device assembly of claim 1 , wherein each metallic bonding material composition of the multiple bonded material portions is a binary eutectic compound composition.
10. The device assembly of claim 9 , wherein:
the common metal is Sn; and
each of the unique elements is selected from In, Cu, Zn, Au, Ag, Al, Re, Pd, Ge, Ni, Ti, Cr, and Nb.
11. The device assembly of claim 9 , wherein:
the common metal is In; and
each of the unique elements is selected from Sn, Ag, Au, Cu, Pt, Pd, and Te.
12. The device assembly of claim 9 , wherein:
the common metal is Te; and
each of the unique elements is selected from In, Sn, Ag, Cu, and Ge.
13. The device assembly of claim 9 , wherein:
the common metal is Cu; and
each of the unique elements is selected from In, Sn, Au, Te, Pd, and Pt.
14. The device assembly of claim 1 , wherein each metallic bonding material composition of the multiple bonded material portions has a respective reflow temperature that is different from a reflow temperature of any other of the multiple bonded material portions.