Micro-electromechanical die module with planarized thick film layer

DETAILED DESCRIPTION It is an object of the present invention to provide an improved micro-electromechanical device having two silicon substrates bonded together by an intermediate thick film layer of patterned polymeric material, such as, for example, polyimide, wherein the improvement is achieved by planarizing one surface of the thick film, thereby preventing topographical formations deleterious to bonding strength between the substrates.
It is another object of the invention to substantially prevent the standoff between two bonded substrates of a micro-electromechanical device, such as an ink jet printhead, wherein the two bonded substrates are the heater plate and channel plate of the printhead with a patterned thick film layer sandwiched between, and standoff of the channel plate is prevented by the planarization of the patterned thick film layer using a method having minimal impact to the existing fabrication sequence of the printhead.
In the present invention, improved devices having micro-electromechanical systems (MEMS) are disclosed.
Such MEMS devices generally have two silicon wafers or substrates bonded together by an intermediate, patterned thick film polymeric layer, such as, for example, polyimide.
The patterned features in the thick film layer provide cavities for the housing of electrical and electromechanical devices, such as, pressure sensors, accelerometers, and the like and including liquid flow structures and passageways that are hermetically sealed between the two silicon wafers.
Planarizing the thick film layer to remove protruding topographic formations caused, for example, by the patterning process results in a stronger bond between the wafers, as well as better seals between the wafers and the thick film layer with the patterned recesses.
One example of a MEMS device is an ink jet die module which may be either an "edge shooter" or "roof shooter" type thermal ink jet printhead.
In a roof shooter type printhead, the heater plate has an array of heating elements with addressing electrodes and an opening therethrough for use as an ink inlet