Use of mesa structures for supporting heaters on an integrated circuit
View Patent ↗An integrated circuit is joined to a liquid container. The integrated circuit includes a passivation layer. A resistor is used as a heater to heat fluid in a liquid container. A mesa structure is formed over the passivation layer. The mesa structure is in contact with the resistor and is used to more effectively deliver heat from the resistor to the liquid container.
1. An optical switch comprising a planar light circuit (PLC), an integrated circuit (IC) and a mesa structure, the PLC comprising a waveguide and being joined to the IC, the mesa structure being interposed between the PLC and a top surface of the IC, a trench being formed in the underside of the PLC and filled with a liquid, the trench intersecting the waveguide at a cross-point disposed above the mesa structure, the mesa structure being disposed above the IC and separated therefrom by a passivation layer, at least top and bottom resistive layers being formed atop the mesa structure and operably connected to metal leads corresponding thereto, the top and bottom resistive layers being separated by an insulating layer disposed therebetween, a first portion of bottom resistive layer not covered by the metal leads having an area larger than a second portion of the top resistive layer not covered by metal leads, the top and bottom resistive layers being configured to heat the liquid in the trench and thereby effect a change in an index of refraction of the liquid in response to electrical current passing through the top and bottom resistive layers, at least portions of the mesa structure projecting upwardly above the passivation layer and the top surface of the IC, wherein at least a portion of the bottom resistive layer is conformably disposed above the projecting portion of the mesa and thereby placed within close proximity to the liquid in the trench to effect efficient heating of the liquid.
2. The optical switch of claim 1 , wherein the mesa structure comprises pyrolytic material.
3. The optical switch of claim 1 , wherein the mesa structure comprises sputtered silicon.
4. The optical switch of claim 1 , wherein the mesa structure comprises TEOS.
5. the optical switch of claim 1 , wherein electrical connections are established to the top and bottom resistive layers through metal leads formed above the mesa structure.
6. The optical switch of claim 1 , wherein the mesa structure has a maximum thickness of about one micron.
7. The optical switch of claim 1 , wherein the PLC is joined to the IC by at least one of wafer bonding and soldering.
8. The optical switch of claim 1 , wherein at least one of the top resistive layer and the bottom resistive layer comprises aluminum, tantalum or tantalum aluminum.
9. The optical switch of claim 1 , wherein the bottom resistive layer is configured to assist heating of the top resistive layer during a burn-in period.
10. The optical switch of claim 1 , wherein at least one of the top resistive layer and the bottom resistive layer is configured to form a bubble in the liquid when electrical current is passed therethrough.