Thermal ink jet printhead

Claim 2

A thermal ink jet recording apparatus for ejecting and propelling ink droplets on demand along a flight path toward a recording medium spaced therefrom in response to electrical input signals representing digitized data signals applied thereto, comprising: at least one elongated straight channel defining a straight ink flow path therethrough and having an orifice on one end substantially perpendicular to the ink flow path, the other end serving as an inlet in communication with an ink reservoir; means for filling and maintaining the reservoir and channel with ink having a predetermined pressure, the channel and orifice being dimensioned to cause a meniscus to be formed at the orifice that has a surface tension which prevents ink from weeping therefrom; a heating element being located internally of the channel and having a predetermined surface area contacting the ink, the surface of the heating element being perpendicular to the ink flow path in the channel, the heating element being positioned at the bottom of a recess of predetermined uniform depth in a surface portion of the channel, said recess having walls that closely surround the heating element and that are substantially perpendicular thereto, said recess being positioned closely adjacent said orifice a predetermined distance upstream thereof; means for applying current pulses to the heating element in said recess in response to the input signals, the pulses each having sufficient amplitude and duration to vaporize momentarily the ink contacting the heating element surface substantially instantaneously to form a temporary vapor bubble which causes the expulsion of a discrete droplet of ink from said orifice in a direction in substantial alignment with the ink flow path in said straight channel and propels it towards the recording medium, the walls of the recess containing the heating element inhibiting the growth of the bubble in a direction parallel to said ink flow path and said surface of the heating element, while promoting bubble growth in a direction normal to the surface of the heating element, and thus preventing a release of vaporized ink from the bubble during the droplet expulsion with a consequent ingestion of air, so that the operational efficiency of the printhead is improved; and the ink from the reservoir replenishing the ink in the channel by capillary action each time a droplet is expelled.

Claim 3

The ink jet recording apparatus of Claim 1, wherein the recess has a depth in the range of 10 to 100 microns.

Claim 4

The ink jet recording apparatus of Claim 1 or Claim 2, wherein the heating element surface area is about 50 by 100 microns (2 mils by 4 mils).

Claim 5

The ink jet recording apparatus as claimed in any preceding claim, wherein the recessed heating element is located approximately 50 to 75 microns upstream from said orifice.

Claim 6

A thermal ink jet printhead for ejecting and propelling ink droplets on demand therefrom along a flight path from orifices in the printhead toward a recording medium spaced therefrom by momentarily heating ink located in straight capillary channels within the printhead that interconnect respective ones of the orifices with an ink supplying reservoir also within the printhead, thus forming a straight ink flow path therebetween to produce temporary vapor bubbles in the channels, the heating of the ink being in response to electrical input signals representing digitized signals selectively applied to individual heating elements located one each in the channels adjacent the orifices, the printhead comprising: an upper substrate having first and second parallel surfaces and two opposing, parallel edge faces that are perpendicular to the substrate surfaces, the first surface containing a depression and a plurality of parallel straight grooves, one end of the grooves perpendicularly penetrating one upper substrate face and the other ends of the grooves opening into the depression; a lower substrate having first and second parallel surfaces and an edge face perpendicular to the lower substrate surfaces, a plurality of heating elements being formed in a row on the lower substrate first surface parallel with and a predetermined distance from the lower substrate face, together with respective electrodes for selectively addressing the heating elements with said electrical input signals, the addressing electrodes having terminal ends at the edges of the lower substrate first surface other than the one adjacent its edge face; a passivation layer covering the lower substrate first surface, including said addressing electrodes, but excluding the heating element and the terminal ends of the addressing electrodes, these having been cleared of the passivation layer; a thick film insulative layer having a predetermined thickness overlaying only the passivation layer, so that the thickness of the thick film layer provides substantially perpendicular walls that individually surround each of the heating elements, thus placing each heating element at the bottom of a recess produced by said thick film walls; said upper and lower substrate being aligned and bonded together to form the printhead with their respective first surfaces being confrontingly joined and with the upper substrate face having the groove penetrations being coplanar with the lower substrate face, so that the upper substrate depression and grooves respectively become the ink reservoir and the ink channels, the groove penetrations in the upper substrate face become the orifices, the alignment of the upper and lower substrates places one recessed heating element in each channel a predetermined distance from an associated orifice, so that the thick film walls inhibit the growth of the vapour bubbles in a direction parallel with the ink flow path in said channels while promoting bubble growth in a direction normal to the heating elements, whereby the heating element recess in said thick film layer prevents vaporized ink blowout during said droplet ejecting bubble generation; means for connecting the printhead reservoir to a source of ink under a predetermined pressure external to the printhead; and means for addressing the electrode terminal ends with said input signals.

Claim 7

A thermal ink jet printhead for ejecting and propelling ink droplets on demand therefrom along a flight path from orifices in the printhead toward a recording medium spaced therefrom by momentarily heating ink located in straight capillary channels within the printhead that interconnect respective ones of the orifices with an ink supplying reservoir also within the printhead, thus forming a straight ink flow path therebetween to produce temporary vapor bubbles in the channels, the heating of the ink being in response to electrical input signals representing digitized signals selectively applied to individual heating elements located one each in the channels adjacent the orifices, the printhead comprising: an upper substrate having first and second parallel surfaces and two opposing, parallel edge faces that are perpendicular to the substrate surfaces, the first surface containing a depression and a plurality of parallel straight grooves, one end of the grooves perpendicularly penetrating one upper substrate face and the other ends of the grooves opening into the depression; a lower substrate having first and second parallel surfaces and an edge face perpendicular to the lower substrate surfaces, a plurality of heating elements being formed in a row on the lower substrate first surface parallel with and a predetermined distance from the lower substrate face, together with respective electrodes for selectively addressing the heating elements with said electrical input signals, the addressing electrodes having terminal ends at the edges of the lower substrate first surface other than the one adjacent its edge face; a passivation layer covering the lower substrate first surface, including said addressing electrodes, but excluding the heating element and the terminal ends of the addressing electrodes, these having been cleared of the passivation layer; a thick film insulative layer having a predetermined thickness overlaying only the passivation layer, so that the thickness of the thick film layer provides substantially perpendicular walls that individually surround each of the heating elements, thus placing each heating element at the bottom of a recess produced by said thick film walls; said upper and lower substrate being aligned and bonded together to form the printhead with their respective first surfaces being confrontingly joined and with the upper substrate face having the groove penetrations being coplanar with the lower substrate face, so that the upper substrate depression and grooves respectively become the ink reservoir and the ink channels, the groove penetrations in the upper substrate face become the orifices, the alignment of the upper and lower substrates places one recessed heating element in each channel a predetermined distance from an associated orifice, so that the thick film walls inhibit the growth of the vapour bubbles in a direction parallel with the ink flow path in said channels while promoting bubble growth in a direction normal to the heating elements, whereby the heating element recess in said thick film layer prevents vaporized ink blowout during said droplet ejecting bubble generation; means for connecting the printhead reservoir to a source of ink under a predetermined pressure external to the printhead; and means for addressing the electrode terminal ends with said input signals.

Claim 8

The ink jet printhead of Claim 5, wherein the thick film layer has a uniform thickness in the range of 10 to 100 microns to produce said recesses having a depth of this range; wherein the thick film layer is Riston (Trade Mark); and wherein the recessed heating elements are located approximately 50 to 75 microns upstream from said orifices.