The invention relates to a microinjector head and its manufacturing method, and more particularly, to an integrally formed microinjector head with driving circuit, and a manufacturing method thereof.

At present, droplet injectors are widely applied in inkjet printers. Droplet injectors also have many other applications in different fields such as fuel injection systems, cell sorting, drug delivery systems, direct print lithography and micro jet propulsion systems. The common aim of the above applications is to provide a droplet injector that is reliable, of low-cost, and provides high-quality droplets with a high frequency and a high spatial resolution.

However not all apparatuses can successfully inject uniform droplets. In currently known and used droplet injection systems, one system using thermally driven bubbles to inject droplets is proved to be a successful system because of its comparatively simple architecture and lower cost.

U. S. Pat. No. 6,102,530-"Apparatus and method for using bubbles as virtual valve in microinjector to eject fluid" mentions a droplet injection apparatus with virtual valves as shown in Fig. 1. In fig.1, heaters 20, 22 are located around orifices 18. A first bubble is generated at a position on a fluid chamber 14 close to orifices upon heating, the first bubble acts like a virtual valve and is capable of reducing a cross talk effect with the adjacent chambers. A second bubble is then generated and approaches the first bubble to push the fluid, causing a droplet to be ejected from the orifice 18. Finally, the second bubble fuses with the first bubble and successfully reduces the production of satellite droplets.

U. S. Pat. No. 5,122,812-"Thermal inkjet print head having driver circuit thereon and method for making the same" mentions a structure of an inkjet print head with driving circuit as shown in Fig. 2. Heating devices and driving circuit are integrated on a same substrate. However there are still many steps in the process. And according to the structure, a barrier layer 130 of 20 ~ 30 µm in thickness must be formed and an orifice plate is adhered on the barrier layer 130. This adhesion procedure limits the spatial resolution due to unavoidable assembly tolerance. In addition, the adhesion procedure is not compatible with general IC processes. When microinjector arrays are integrated with driving circuit to reduce layout and are tightly packed, such incompatibility problems become more obvious and lead to more complicated manufacturing processes and thus higher costs.

It is therefore a primary objective of the claimed invention to provide a microinjector head with driving circuit to control a plurality of first and second bubble-generating devices simultaneously to eject fluid in a plurality of chambers from orifices. A secondary objective of the claimed invention is to provide a manufacturing method for making a microinjector head with driving circuit in fewer steps and with less number of circuit devices and linking circuits as compared with the conventional microinjector head.

According to the claimed invention, the microinjector head with driving circuit to eject fluid uses a bubble as a virtual valve. The microinjector head comprises a plurality of fluid chambers, a manifold, a plurality of orifices, and a plurality of pairs of bubble generators, each pair of bubble generators comprising a first bubble generating device and a second bubble generating device, and a driving circuit.

Wherein the manifold is communicated with the fluid chambers and the plurality of orifices are communicated with the fluid chamber.

The first and second bubble generating device are located near a corresponding orifice and above the corresponding chamber, the first bubble-generating device generates a first bubble that is used as a virtual valve, thereafter, the second bubble-generating device generates a second bubble to cause fluid in the chamber to eject out from the orifice when the chamber is filled with fluid.

The driving circuit comprises a plurality of functional devices disposed on a same substrate as the plurality pairs of first and second bubble generating devices. The driving circuit is used to independently send a driving signal to a single bubble generator, and to drive the plurality pairs of the bubble generators, whereby functions to simultaneously control the plurality pairs of the bubble generators.

According to the claimed invention, it is provided a method for manufacturing the microinjector with a driving circuit comprising the steps of providing a substrate; forming a driving circuit which includes a plurality of functional devices on the substrate; then either forming a sacrificial layer on the substrate without coving the driving circuit or using the uppermost layer of the dielectric layer upon forming the driving circuit as the sacrificial layer; sequentially, forming a low-stress material layer on the sacrificial layer; then, etching the substrate and the sacrificial layer to form a manifold and a plurality of fluid chambers wherein the manifold is communicated with the fluid chambers so as to supply the fluid to the fluid chambers.

Then, a plurality of pairs of first and second bubble generating device are formed on the low-stress material layer while communicating with the driving circuit. Finally, a plurality of orifices are formed between the corresponding first and second bubble generating device, and communicated with the fluid chambers to eject the fluid, whereby an integrally formed microinjector with a driving circuit is finished.

These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

• Fig. 1 is a structural diagram of a prior art droplet injection apparatus with virtual valves.
• Fig. 2 is a structural dissection diagram of a prior art microinjector head with driving circuit;
• Fig. 3 to Fig. 9 are structural and schematic diagrams of procedures to manufacture the microinjector head with driving circuit and structural diagrams of the microinjector head, wherein Fig. 9 is a structural and schematic diagram of the microinjector head with driving circuit of the present invention; and
• Fig. 10 to Fig.12 are structural and schematic diagrams of a second embodiment of procedures to manufacture the microinjector head with driving circuit and structural diagrams of the microinjector head.

10

array

12

microinjector

14

fluid chamber

16

manifold

18

orifice

20

first heater

22

second heater

24

common electrode

26

fluid

38

substrate

40

sacrificiallayer

42

low-stress layer

44

conductive layer

45,46

low temperature oxide layer

50

second part

51

dielectric layer

52

first part

101

thin oxide layer

102

silicone nitride layer

105

polysilicon gate

106

source

107

drain

130

shield layer

140

orifice plate

The present invention offers an improvement over the prior art. Therefore, references to items shown in Fig.1 and Fig.2 will be made in the following description. As shown in Fig.1 which shows an array 10 of microinjector 12, the array 10 comprises a plurality of microinjectors 12 adjacent each other. Each of the microinjectors includes a fluid chamber 14, a manifold 16, an orifice 18, a first heater 20, and a second heater 22. The first heater 20 and the second heater 22 are connected in series to a common electrode 24.

The first heater 20 and the second heater 22 is operated, so that the first heater 20 generates a first bubble which functions like a valve, for separating the fluid chamber 14 and the orifice 18, and the second heater 22 then generates a second bubble which is used to push the fluid 26, cause the fluid to be ejected from the orifice 18, thereby achieve the function of ejecting fluid 26.

The fluid chamber 14 is filled with fluid 26 which includes but not limited to ink, gasoline, oil, chemicals, biomedical solution, water and the like, and the kind of the fluid is selected depending on the special application.

However, in the present invention, in order to simultaneously control a plurality of pairs of the first and second heater 20 and 22, it is necessary to incorporate a driving circuit into the microinjector head.

As shown in Figs. 3 to Fig. 5, making a microinjector array 10 with driving circuit on a substrate 38 such as a silicon wafer comprises forming a thin oxide layer 101 on the substrate 38, then forming a silicon nitride (SiN_x) layer 102 on the thin oxide layer (as shown in Fig. 3), etching the silicon nitride layer 102 (as shown in Fig. 4) after exposing and developing a silicon nitride layer 102, , and then using local oxidation to oxidize unprotected regions of the thin oxide layer 101 to form a field oxide layer. Until now, a dielectric layer 51 (as shown in Fig. 5) which comprised a first part 52 and a second part 50 is formed. The first part 52 is a part of the thin oxide layer 101 covered by silicon nitride layer 102. The second part 50 is the field oxide layer formed by local oxidation. This field oxide layer can be etched in the following procedures to form fluid chambers 14. Then the silicon nitride layer 102 is removed. Blanket boron ion implantation of the first part 52 and the second part 50 (as shown in Fig. 5) adjusts the threshold voltage of the driving circuit. A polysilicon gate 105 is formed on the first part 52 and a phosphorus ion implantation of the polysilicon gate 105 is performed to reduce resistance of the polysilicon gate 105. Implanting arsenic ions in the substrate 38 forms a source 106 and a drain 107 close to the gate 105. Therefore, a plurality of functional devices are formed on the substrate 38 (as shown in Fig. 6).

Please refer to Fig. 7. A low stress layer 42, such as SiN_x, is deposited on the second part 50 as an upper layer of chambers 14.

Please refer to Fig. 8. An etching solution KOH is used to etch a back side of the substrate 38 to form a manifold 16 as a main channel for fluid supply, and then the second part 50 is removed by the etching solution HF. Another etching using KOH is performed under precisely controlling the etching period to increase the depths of the fluid chambers 14. So the chambers 14 and the manifold 16 are connected and are capable of being filled with fluid. Extra care must be undertaken during this etching step because the convex comers of the chambers 14 are also attacked and rounded.

Heaters, including first heaters 20 and second heaters 22 are deposited and patterned. Preferably, the first heaters 20 and the second heaters 22 may be made of an alloy of tantalum and aluminum. However, other materials or alloys, such as platinum or HfB₂, may also be employed to achieve the same effect. To protect the first heaters 20 and the second heaters 22 and isolate the plural functional devices, a low temperature oxide layer 45 is deposited as a protection layer on the whole substrate 38 which includes the gate 105, the source 106, the drain 107, and the second part 50.

A conductive layer 44 is formed on the first heaters 20 and the second heaters 22 to connect the first heaters 20, the second heaters 22, and the functional devices of the driving circuit. The driving circuit can transmit independently driving signals to a single heater (the first heaters 20 and the second heaters 22) and drive a plurality of pairs of heaters (the first heaters 20 and the second heaters 22), whereby less circuit elements and circuit lines are required to achieve the same function. For example, in the preferred embodiment, the first heaters 20 and the second heaters 22 are connected in series. The driving circuit controls the plurality bubble generators in matrix manner. For example, a column bubble generators is powered simultaneously, and another row is inputted transmission signals (or information), to independently control a single first heater 20 and second heater 22. The conductive layer 44 may preferably be made of an alloy of aluminum-silicon-copper. The conductive layer 44 may also be made of aluminum, copper, gold, tungsten, or other materials. Afterwards, a low temperature oxide layer 46 is deposited as a protection layer on the conductive layer 44.

Please refer to Fig. 9. An orifice 18 is formed between the first heater 20 and the second heater 22. If a line width of 3 µm is allowed in photolithography, the diameter of the orifice 18 can be as small as 2 µm, and the pitch between the orifice 18 and an adjacent orifice 18 can be as small as 15 µm. Until now, an integrally formed microinjector array with driving circuit is formed. Not only the driving circuit and heaters are integrated on the same substrate 38, but also an integral microinjector head structure is formed without the need of adhesion of an orifice plate.

The following is a description of another embodiment of the present invention. Compared with the first embodiment, the difference lies in the process of directly etching the second part 50 of Fig. 6 to form the fluid chamber 14 in the above mentioned embodiment as shown in Figs. 7, 8, and 9. This embodiment first etches a part of the second part 50 and forms a sacrificial layer 40 on the etched position, then performs the subsequent processes. Please refer to Fig. 10. Fig. 10 continues the process of Fig. 6. A part of the second part 50 of Fig. 6 is etched locally, and an oxide layer 40 is deposited on a part of the substrate 38 uncovered by the driving circuit so as to become a sacrificial layer 40 of the fluid chamber 14. A low stress layer 42' is then deposited as a top layer of the chamber 14.

Please refer to Fig. 11 and Fig. 12, which are similar in their processes to those of Fig. 8 and Fig. 9. As shown in Fig. 11, the substrate 38 and the sacrificial layer 40 are etched from the back side to form the manifold 16 and the chambers 14. The first heater 20, the second heater 22 and the protective low temperature oxide layer 45 are then deposited. A conductive layer 44 is formed to conduct the first heater 20, the second heater 22, and the driving circuit, and a low temperature oxide layer 46 is deposited on the conductive layer 44 as a protective layer. Finally, as shown in Fig. 12, photolithography is utilized to form an orifice 18 between the first heater 20 and the second heater 22. Then an integrally formed microinjector array with driving circuit is formed.

The order of the above processes can be changed according to real situations while still manufacturing a micro droplet injector head with appropriate driving circuit.

The microinjector and the method thereof according to the present invention function as follows:

• 1. The present invention provides an improved micro-droplet injector structure which can be applied in various fields such as ink jet printer;
• 2. The present invention provides an integrally formed micro-droplet injector in which the driving circuit and heaters are integrated on the same substrate, and the need of orifice plate is eliminated;
• 3. The number of steps is reduced, and the manufacturing process can be simplified;
• 4. The number of the connection wiring is reduced due to an integral structure, thus the manufacturing cost can be lowed while achieving the same control function.

Those skilled in the art will readily observe that numerous modifications and alterations of the present invention may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of appended claims.