Integration techniques for micromachined pMUT arrays and electronics using solid liquid interdiffusion (SLID)
The present disclosure provides methods to integrate pMUT arrays with an ASIC using solid liquid interdiffusion (SLID). In an aspect, the present disclosure provides a device comprising a first substrate and a second substrate, the first substrate comprising a pMUT device and the second substrate comprising an electrical circuit, wherein the first substrate and the second substrate are bonded together using a conductive bonding pillar, which conductive bonding pillar comprises one or more intermetallic compounds. In another aspect, the present disclosure provides a device comprising a first substrate and a second substrate, the first substrate comprising a pMUT device and the second substrate comprising an electrical circuit, wherein the first substrate and the second substrate are bonded together using a conductive bonding pillar, wherein the bonding is performed at a temperature less than the melting point of the conductive bonding pillar after the bonding.
1 . A device comprising at least one first substrate and a second substrate, the first substrate comprising a piezoelectric micromachined ultrasonic transducer (pMUT) device and the second substrate comprising at least one electrical circuit, wherein the first substrate and the second substrate are bonded together using a conductive bonding pillar and a conductive receiver pad, which conductive bonding pillar comprises a layered arrangement of a layer of a first metal or metal alloy between the second substrate and a layer of a second metal or metal alloy distinct from the first metal or metal alloy, and which conductive receiver pad comprises a layer of a third metal or metal alloy that is disposed on the first substrate and distinct from both the first metal or metal alloy and the second metal or metal alloy, wherein a melting temperature of the second metal or metal alloy is (i) less than a melting temperature of the first metal or metal alloy and (ii) less than a melting temperature of the third metal or metal alloy, and wherein the conductive bonding pillar is connected to the conductive receiver pad with the second metal or metal alloy being in contact with the third metal or metal alloy to form one or more solid liquid interdiffusion (SLID) bonds in a SLID bonding process between the second metal or metal alloy and the third metal or metal alloy, wherein the bonding comprises die-to-wafer bonding a plurality of singulated first substrates, each comprising a pMUT device, to the second substrate.
2 . The device according to claim 1 , wherein the bonding is performed at a temperature less than a melting temperature of the conductive bonding pillar after the bonding.
3 . The device according to claim 1 , wherein the pMUT device is configured to perform ultrasound imaging.
4 . The device according to claim 1 , wherein the die-to-wafer bonding uses an intermediate handle substrate and a temporary bonding layer.
5 . The device according to claim 4 , wherein the bonding comprises:
(a) temporarily bonding a wafer of the first substrate to the handle substrate using the temporary bonding layer;
(b) dicing the wafer on the handle substrate; and
(c) bonding the diced wafer to another wafer of the second substrate using solid liquid interdiffusion (SLID).
6 . The device according to claim 1 , wherein the bonding forms a hermetic sealed cavity, which cavity is configured to controllably maintain gas species and pressure.
7 . The device according to claim 1 , wherein the conductive bonding pillar has a height of at least 3 μm.
8 . The device according to claim 1 , wherein the conductive bonding pillar has a lateral dimension between 10 μm and 100 μm.
9 . The device according to claim 1 , wherein the SLID bonding is performed at a temperature of no more than 300° C.
10 . The device according to claim 1 , wherein the SLID bonding comprises bonding together a plurality of different metals or metal alloys selected from the group consisting of silver (Ag), gold (Au), copper (Cu), indium (In), nickel (Ni), tin (Sn), Cu-Sn, Au-Sn, Au-In, Au-In-Ni, and Ni-Sn.
11 . The device according to claim 1 , wherein one or more resultant intermetallic compounds are formed in the one or more solid liquid interdiffusion (SLID) bonds.
12 . The device according to claim 1 , wherein two or more resultant intermetallic compounds are formed in the one or more solid liquid interdiffusion (SLID) bonds.
13 . The device according to claim 1 , wherein the conductive bonding pillar further comprises a fourth metal or metal alloy, distinct from the first metal or metal alloy, the second metal or metal alloy, and the third metal or metal alloy, disposed between the second substrate and the first metal or metal alloy.
14 . The device according to claim 1 , wherein the second metal or metal alloy is a metal and is Sn, and wherein the third metal or metal alloy is a metal and is Au.
15 . The method according to claim 1 , wherein the first substrate comprising the pMUT is a known good die (KGD).
16 . The method according to claim 1 , wherein the first substrate and the second substrate have mismatched coefficients of thermal expansion (CTE).
17 . A method of fabricating an integrated device, the method comprising:
(a) obtaining at least one first substrate comprising a piezoelectric micromachined ultrasonic transducer (pMUT) device;
(b) obtaining a second substrate comprising at least one electrical circuit; and
(c) bonding together the first substrate and the second substrate using at least one conductive bonding pillar and at least one conductive receiver pad, which at least one conductive bonding pillar is disposed on the second substrate and comprises a layered arrangement of a layer of a first metal or metal alloy between the second substrate and a layer of a second metal or metal alloy, wherein the second metal or metal alloy is distinct from the first metal or metal alloy and has a melting temperature that is lower than a melting temperature of the first metal or metal alloy, and which at least one conductive receiver pad is disposed on the first substrate and comprises a layer of a third metal or metal alloy that is disposed on the first substrate and distinct from both the first metal or metal alloy and the second metal or metal alloy, wherein the conductive bonding pillar is connected to the conductive receiver pad with the second metal or metal alloy being in contact with the third metal or metal alloy to form one or more solid liquid interdiffusion (SLID) bonds are by a SLID bonding process between the second metal or metal alloy and the third metal or metal alloy, wherein the bonding comprises die-to-wafer bonding a plurality of singulated first substrates, each comprising a pMUT device, to the second substrate.
18 . The method of claim 17 , wherein the bonding is performed at a temperature less than the melting temperature of the conductive bonding pillar after the bonding.
19 . The method according to claim 17 , wherein the pMUT device is configured to perform ultrasound imaging.
20 . The method according to claim 17 , wherein the die-to-wafer bonding uses an intermediate handle substrate and a temporary bonding layer.
21 . The method according to claim 20 , wherein the bonding comprises:
(a) temporarily bonding a wafer of the first substrate to the handle substrate using the temporary bonding layer;
(b) dicing the wafer on the handle substrate; and
(c) bonding the diced wafer to another wafer of the second substrate using solid liquid interdiffusion (SLID).
22 . The method according to claim 21 , wherein the method further comprises:
(a) aligning the diced wafer to the other wafer of the second substrate;
(b) adjusting atmospheric conditions;
(c) applying pressure to establish contact between the diced wafer and the other wafer; and
(d) raising the temperature to form one or more SLID bonds.
23 . The method according to claim 21 , wherein the method further comprises
(a) removing the handle substrate and the temporary bonding layer;
(b) dicing the other wafer of the second substrate; and
(c) producing individual die of the first substrate bonded to individual die of the second substrate.
24 . The method according to claim 21 , wherein the method further comprises thinning the first substrate or the second substrate.
25 . The method according to claim 17 , wherein the bonding forms a hermetic sealed cavity, which cavity is configured to controllably maintain gas species and pressure.
26 . The method according to claim 17 , wherein the conductive bonding pillar has a height of at least 3 μm.
27 . The method according to claim 17 , wherein the conductive bonding pillar has a lateral dimension between 10 μm and 100 μm.
28 . The method according to claim 17 , wherein the SLID bonding process is performed at a temperature of no more than 300° C.
29 . The method according to claim 17 , wherein the SLID bonding comprises bonding together a plurality of different metals or metal alloys selected from the group consisting of silver (Ag), gold (Au), copper (Cu), indium (In), nickel (Ni), tin (Sn), Cu-Sn, Au-Sn, Au-In, Au-In-Ni, and Ni-Sn.
30 . The method of claim 17 , wherein the one or more SLID bonds connect the conductive bonding pillar and the conductive receiver pad in a conductive bond that comprises a single layer of a new alloy formed during creation of the SLID bond.
31 . The method of claim 17 , wherein the bonding together the first substrate and the second substrate uses at least a first conductive bonding pillar and a second conductive bonding pillar and at least a first conductive receiver pad and a second conductive receiver pad, and wherein a first SLID bond is formed between the first conductive bonding pillar and the first conductive receiver pad and a second SLID bond is formed between the second conductive bonding pillar and the second conductive receiver pad.