Heater stack and method for making heater stack with cavity between heater element and substrate

1. A heater stack for a micro-fluid ejection device, comprising:

first strata configured to support and form a fluid heater element responsive to repetitive electrical activation and deactivation to produce repetitive cycles of ejection of a fluid from an ejection chamber above said fluid heater element; and

second strata overlying said first strata and contiguous with said ejection chamber to provide protection of said fluid heater element;

wherein said first strata includes

a substrate having a front surface and a rear surface with a cavity extending into the substrate for a given depth from the front surface toward the rear surface,

a heater substrata overlying said cavity and substrate, and

a residual decomposed layer of sacrificial material in the cavity resulting from processing out of the cavity a sacrificial material thereby leaving said cavity substantially empty of said sacrificial material such that during repetitive electrical activation said cavity enables said fluid heater element to transfer heat energy into the fluid in said ejection chamber for producing ejection of the fluid therefrom substantially without transferring heat energy into said substrate.

2. The heater stack of claim 1 wherein said sacrificial material is an exposed and developed photo-imagable photoresist material.

3. The heater stack of claim 2 wherein said photo-imagable photoresist material is a photosensitive polymer treated with a photoacid.

4. The heater stack of claim 1 wherein said cavity is gas-filled.

5. The heater stack of claim 1 wherein said heater substrata and second strata overlying said heater substrata have slots formed along a pair of opposite lateral sides of said fluid heater element through said heater substrata and said second strata which provide fluid communication between said ejection chamber above said fluid heater element and said cavity below said fluid heater element permitting the fluid in said ejection chamber to flow between said ejection chamber and said cavity such that said cavity is filled with the same fluid as is ejected from said ejection chamber by said fluid heater element.

6. The heater stack of claim 5 wherein said heater substrata includes: a resistive layer overlying said cavity and substrate; and

a conductive layer having an anode portion and a cathode portion separated from one another by a space and overlying and deposited on lateral portions of said resistive layer being interconnected and separated by a central portion of said resistive layer deposed under said space of said conductor layer so as to define said fluid heater element.

7. The heater stack of claim 6 wherein said heater substrata further includes a protective layer between said substrate and resistive layer so as to overlie said cavity and protect an underside of said fluid heater element from prolonged contact with the fluid in said cavity, said slots also being formed through said protective layer of said heater substrata.

8. The heater stack of claim 7 wherein said second strata includes a protective layer overlying said anode and cathode portions of said conductor layer and also overlying said central portion of said resistive layer defining said fluid heater element of said heater substrata, said slots also being formed through said protective layer of said second strata.