Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-10-15
2001-11-27
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S054000, C347S063000, C216S027000
Reexamination Certificate
active
06322202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of heating apparatuses for microdevices, the method of fabricating such heating apparatuses and their methods of use, and more particularly to processes, structures and materials for the construction and use of ink-jet print heads, other microinjection devices, microelectromechanical devices and chemical analysis devices.
2. Description of the Related Art
A very common device in use today is the ink-jet print head. Ink-jet printers are superior to dot matrix printers, being able to print in multiple colors, with less noise and with better print quality.
The thermal ink-jet print head is a specific example of a structure that is representative of the class of microinjection devices, which are devices which expel small, controlled amounts of a liquid, thereby injecting the liquid into the target. In general, the ink-jet print head has a plurality of discrete micro-injectors, formed in an array, each with an orifice, or nozzle, of small diameter. Upon receiving an electrical signal, the electricity is used to heat a liquid to expand or vaporize it, expelling ink through the nozzle and onto the paper.
An exemplary ink-jet print head generally contains a heater section in which a heater resistor layer is formed on a substrate and an electrode layer is formed on the heater resistor layer to provide electrical contact. This heater section heats a working fluid which vaporizes, expanding a membrane which drives the expulsion of an ink drop. I have noticed that this ink-jet printer head design, however, is subject to several problems. First, the heater resistor layer and electrode layer are generally made of different materials, and adhesion between these layers can be weak. Chemical reactions occurring in the etching process used to pattern the layers can lead to gradual deterioration of the adhesion zone between the two layers. As a result, a gap can form between the layers. Secondly, during use, the working liquid contacting these layers may seep into the gap between the two layers, causing further deterioration. Thirdly, the mechanical stress caused by the vibration of the membrane can also cause deterioration of the contact between the layers. When such a gap forms, it leads to irregularities in the vapor pressure of the working liquid. This in turn causes irregularities in the vibration of the membrane and leads to poor formation of the ink drop and thus poor performance of the print head.
An example of earlier efforts to address a related problem is U.S. Pat. No. 5,223,855, to Ota et al., entitled Thermal Head For A Printer. This deals with the deformation of a thermal head due to the difference in thermal expansion between members and describes use of a soft adhesive to adhere the substrate containing the heating elements to a support board. This use of adhesive does not solve, however, the problem of adhesion of the electrodes to the heating resistor.
I have observed that what is needed, then, is a method for insuring that the adhesion of the electrodes to the heater resistor is robust, and has a long lifetime in devices such as ink-jet print heads.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved heating apparatus and process for fabricating and using a heating apparatus to be used in microinjection devices.
It is a further object of the invention to provide a heating apparatus with a heater resistor layer and electrode layer that are firmly adhered together so that the heater resistor layer and the electrode layer resist separation.
It is a still further object to prevent gap formation between the electrode layer and heater resistor layer in heating devices, thereby creating more robust and longer lived devices
It is a yet further object to provide an improved microinjection device incorporating the heating apparatus of the present invention.
It is a still yet further object to provide a method of manufacture of the heating apparatus of the present invention that yields an improved heating apparatus which is more robust and longer-lived.
It is another object to provide methods of use of the heating apparatus of the present invention to yield improved devices for microinjection of liquids, improved micromechanical devices, and improved devices for chemical analysis.
These and other objects may be attained with the use of a separate adhesion layer disposed between a heater resistor layer and an electrode layer during fabrication of microinjection devices. According to one aspect of the present invention, there is provided a heating apparatus for a microinjection device having a substrate with a protection film; a heater resistor layer formed on the protection film; an electrode layer formed on the heater resistor layer with an electrode pad delivering electrical energy applied from an external device; an adhesion layer inserted between the heater resistor layer and electrode layer; and a heater chamber barrier layer formed on the electrode layer to define a heater chamber that contacts the heater resistor layer. Preferably, the heater resistor layer is made of TiB
2
, and the adhesion layer is made of vanadium, chromium, or nickel.
According to another aspect of the present invention, there is provided a method for fabricating a heating apparatus for a microinjection device by forming a protection film on a substrate and forming a heater resistor layer on the protection film; depositing an adhesion layer on the heater resistor layer; depositing a first electrode as a layer on the adhesion layer; depositing a second electrode as a layer on the first electrode; forming an electrode pad on the second electrode, and etching and patterning the adhesion layer, the first electrode and the second electrode. A heater chamber barrier layer is formed on the second electrode and the heater chamber barrier layer is patterned to form a heater chamber on the heater resistor layer.
Preferably, the adhesion layer is deposited by a sputtering method and has a thickness within the range of approximately 0.1 &mgr;m to 0.2 &mgr;m, and more preferably about 0.15 &mgr;m, and a surface resistance within the range of approximately 180 &OHgr;/cm
2
to 220 &OHgr;/cm
2
, and more preferably about 200 &OHgr;/cm
2
. Preferably, the electrode pad is formed into a thickness within the range of approximately 0.4 &mgr;m to 0.8 &mgr;m, and more preferably about 0.6 &mgr;m. Preferably, the heater chamber barrier layer is formed into a thickness within the range of approximately 10 &mgr;m to 15 &mgr;m, and more preferably about 13 &mgr;m. Here, it is preferable to pattern the heater chamber barrier layer by an ion-plasma etching method.
Preferably, a photoresist adhesion layer is further formed on the heater chamber barrier layer so as to promote adhesion with respect to photoresist, (colloquially referred to as PR). It is preferable to form the photoresist adhesion layer as a single layer consisting of either chromium or copper, or a layer in which chromium and copper are deposited in turn. The photoresist adhesion layer so formed has a thickness within the range of approximately 1.5 &mgr;m to 3 &mgr;m, more preferably about 2 &mgr;m. Preferably, the above-described photoresist adhesion layer is etched by a chemical etching method.
In another aspect of the present invention, there is provided a microinjection device incorporating the heating apparatus of the present invention, fabricated with a substrate having a protection film; a heater resistor layer formed on the protection film; an adhesion layer to promote adhesion between the heater resistor layer and an electrode layer; an electrode layer which contacts the heater resistor layer so as to transmit an electrical signal; a heater chamber barrier layer formed on the electrode layer so as to define a heater chamber which contacts the heater resistor layer; a flexible membrane formed on the heater chamber barrier layer so as to vibrate according to the change in volume of liquid contained in the heater chamber; and
Barlow John
Bushnell , Esq. Robert E.
Mouttet Blaise
Samsung Electronics Co,. Ltd.
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