JP3520864B2 - Inkjet head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head which is a main part of an ink jet recording apparatus, and more particularly to a small and high density ink jet head which uses electrostatic force as its driving force.

[0002]

2. Description of the Related Art An ink jet recording apparatus has many advantages such as extremely low noise during recording, high speed printing, and printing on inexpensive plain paper. The so-called ink-on-demand method, which discharges ink droplets only when necessary for recording, is currently in the mainstream because it does not require recovery of ink droplets unnecessary for recording.

In this ink-on-demand type ink jet head, as shown in Japanese Patent Publication No. 2-51734, the driving means is a piezoelectric element, and as shown in Japanese Patent Publication No. 61-59911. In addition, there is a method of ejecting the ink with a pressure by heating the ink to generate bubbles, and currently, these two methods are mainly put into practical use,
It is widely used in inkjet printers.

However, in the former method using the piezoelectric element, the step of attaching the chip of the piezoelectric element to each vibration plate for generating the pressure in the pressure chamber is complicated. In particular, high-speed and high-quality printing has been required for printing with recent inkjet recording devices. To achieve this, multi-nozzles and high-density nozzles have been manufactured by finely processing piezoelectric elements, It is extremely complicated to bond it to the diaphragm. Further, in order to increase the density, it has become necessary to process the piezoelectric element with a width of several tens to several tens of microns, but the ejection characteristics of each nozzle are unsatisfactory with the size and shape accuracy that can be realized by existing machining. There is a problem that it becomes uniform and the variation in printing quality becomes large, and it is particularly unsuitable as a technique for providing a high-density ink jet head at low cost.

In the latter method of heating ink, the driving means is formed by a thin-film resistance heating element, so that the above-mentioned problems do not exist, but the rapid heating / cooling of the driving means is not possible. There is a problem that the life of the ink jet head is short because the resistance heating element is damaged by repeated or impact when bubbles disappear.

As another effective driving means for solving these problems, a silicon (Si) substrate is etched, a diaphragm and a pressure chamber are integrally formed on the silicon substrate, and they are arranged opposite to each other with a gap on the back surface of the pressure chamber. A conductive substrate is formed, charging and discharging are repeated between the diaphragm and the conductive substrate, the diaphragm is vibrated by the electrostatic force generated there, and the electrostatic force that ejects ink from the nozzle by the pressure change generated in the pressure chamber is driven. An inkjet head used as a force is proposed in USP 4,520,375 and JP-A-2-289351. At present, these methods using electrostatic force as a driving force have not been put into practical use as actuators for inkjet printers, but with the development of micromachining technology in recent years, for example, an implantable type for administration of drugs (insulin) It has gained a great deal of trust as a micropump, and when it is applied to an actuator of an inkjet printer due to its fine and simple structure and long-term reliability, it is easy to miniaturize and increase the density and has a long service life. Can be obtained.

[0007]

However, in order to put the system using electrostatic force as a driving force into practical use as an actuator of an ink jet printer, it can be driven by a power source voltage commonly used as a printer, that is, an information device, and a high printing speed can be achieved. In other words, it is required to be able to drive at a high frequency.
The above-mentioned US Pat. No. 4,520,375 and Japanese Patent Laid-Open No. 2-2.
No. 89351 has not disclosed a structure of an inkjet head that satisfies the above requirements and is of a practical level.

More specifically, in response to the above request, U
In SP 4,520,375, the silicon substrate itself is the structure of the inkjet head, and at the same time, it functions as a passage for passing electricity to the diaphragm, but silicon itself is a semiconductor having a certain electric resistance, and particularly, as a drive circuit. A so-called rectifying contact is likely to be formed at the contact portion of. Since the rectifying contact portion functions as a diode, the movement of the charge is limited to one direction when driving the inkjet head, which is not preferable, and is particularly fatal for speeding up. Further, the electric resistance of silicon itself also increases the time constant during driving, which becomes a factor that hinders high-speed driving. Further, if the density of the head itself is increased, the cross-sectional area of the silicon substrate itself is relatively reduced, and the resistivity is increased accordingly, which is a serious problem. The issue does not make any specific disclosure regarding these points.

On the other hand, in Japanese Unexamined Patent Publication No. 2-289351, an ink flow path and a vibration plate are formed on a silicon substrate, individual electrodes are formed on the vibration plate on the opposite surface of the ink flow path, and silicon itself serves as the vibration plate. Unlike US Pat. No. 4,520,375 in that it is not used as a passage for passing electricity, the electrical characteristics of the silicon itself described above do not hinder high-speed driving of the inkjet head, but the following points are high-speed driving. Is a factor that hinders the implementation of.

That is, if the electrode gap between the individual electrodes on the vibration plate and the common electrode facing them is reduced, dielectric breakdown occurs between the electrodes due to the contact of the electrodes. It must be set large enough to avoid contact, but if the electrode gap is large, a very large voltage is required to bend the diaphragm so that ink is ejected. It is impossible to drive with. In this regard, the same issue attempts to improve the electrostatic force by filling the electrode gap with a ferroelectric substance, but these ferroelectric substances have a fixed crystallographic direction, that is, a high dielectric constant in the solid state. In reality, sufficient vibration cannot be obtained for ejecting ink because the rate is obtained. In addition, since a liquid dielectric material cannot obtain a sufficient dielectric constant, the electrode gap must be made small in the end, so that the viscous resistance of the dielectric liquid becomes extremely large and the response frequency of the diaphragm remarkably decreases. However, it is difficult to drive at a frequency that can be practically used as a head for an inkjet printer, and it has not been put to practical use for the above reasons.

Therefore, the present invention solves the above-mentioned problems in an ink jet head using an electrostatic force as a driving source. First, it can be driven with a low power supply voltage that is commonly used as a printer, and secondly, it has a high printing speed. In other words, it is an object of the present invention to provide a more practical inkjet head that can be driven at a high frequency, in other words, can be driven at a low voltage and at a high speed even when the density of the head is increased.

[0012]

According to another aspect of the present invention, there is provided an ink jet head comprising: a semiconductor substrate integrally formed with a part of a discharge chamber communicating with a nozzle and a vibration plate provided in the part of the discharge chamber; In an inkjet head that stacks a diaphragm and a substrate having electrodes facing each other with a gap, applies an electric pulse between the semiconductor substrate and the electrode, and deforms the diaphragm by the generated electrostatic force to eject ink The semiconductor substrate has a resistivity of 20 Ω · cm or less. Thus, when the inkjet head is driven, an increase in the time constant determined by the resistance value of the semiconductor substrate and the capacitance of the capacitor composed of the vibration plate and the individual electrodes facing the vibration plate is avoided and the time constant is increased. This prevents deterioration of ink ejection characteristics caused by the diaphragm not being able to be sufficiently attracted to the individual electrodes.

[0013]

Further, the first layer is made of chromium (Cr) or titanium (Ti) on a part or all of the surface of the semiconductor substrate having such a resistivity other than the position facing the electrode.
Therefore, a metal film is formed on the second layer with a multilayer film made of gold (Au), rhodium (Rh), or platinum (Pt), or aluminum (Al) or tin (S) is used.
It is preferable to form a single-layer metal film made of n) or indium (In), and drive the metal film and the electrode by connecting a drive circuit. As a result, the contact portion between the metal coating and the semiconductor substrate can be formed with low resistance (ohmic contact) regardless of the polarity of the voltage applied to the metal coating, so that the charge at the contact portion can be smoothly transferred and the resistance can be improved. Since the loss is small and the efficiency is high, it can be driven at a low voltage, and the time constant at the time of driving can be made small, so that the inkjet head can be driven at a high speed, and it is also advantageous for increasing the density of the nozzles.

Further, when the semiconductor substrate is a p-type semiconductor, at least a portion of the surface of the semiconductor substrate where the metal film is formed is doped with a group III element, and when the semiconductor substrate is an n-type semiconductor, the surface of the semiconductor substrate is By doping at least the portion where the metal film is formed with the group V element, the contact portion between the metal film and the semiconductor substrate can be further formed with low resistance.

Further, by forming a plurality of diaphragms on the semiconductor substrate and forming the metal film at equal distances on all the diaphragms, the resistance between the drive circuit and each diaphragm can be made uniform, It is possible to reduce variations in ejection characteristics between nozzles.

[0017]

1 is an exploded perspective view of an ink jet head according to an embodiment of the present invention. The present embodiment shows an example of an edge eject type in which ink droplets are ejected from nozzle holes provided at the end of the substrate, but a face eject ejecting ink droplets from nozzle holes provided at the upper surface of the substrate. You can type. 2 is a sectional side view of the assembled inkjet head, and FIG. 3 is a view taken along the line AA of FIG. The ink jet head 10 of this embodiment is composed of three substrates 1 having the structures described in detail below.
It has a laminated structure in which two and three layers are stacked and joined.

The intermediate first substrate 1 is a silicon substrate, and a plurality of nozzle grooves 1 are formed on the surface of the substrate 1 in parallel at equal intervals from one end so as to form a plurality of nozzle holes 4.
1 and a recess 12 communicating with each nozzle groove 11 and forming a discharge chamber 6 having a diaphragm 5 as a bottom wall;
2 is a narrow groove 13 for an ink inflow port, which will form an orifice 7 provided at the rear of the nozzle 2, and a recessed part, which will form a common ink cavity 8 for supplying ink to each ejection chamber 6. 14 and. Also, the diaphragm 5
A concave portion 15 which constitutes the vibration chamber 9 for mounting an electrode described later is provided in the lower part of the.

In the present embodiment, the facing gap between the diaphragm 5 and the individual electrode arranged opposite thereto, that is, the length G of the gap portion 16 (see FIG. 3, hereinafter referred to as "gap length"). However, the space holding means is formed of the vibration chamber recess 15 formed on the lower surface of the first substrate 1 so that the difference between the depth of the recess 15 and the thickness of the electrode is obtained. Here, the depth of the recess 15 is set to 0.6 μm by etching. The pitch of the nozzle grooves 11 is 0.72 mm and the width thereof is 70 μm.

In the first substrate 1, the first layer is made of Cr or Ti and the second layer is made of Au, Rh or Pt.
The common electrode 17 is formed of a multi-layer metal film made of or a single-layer metal film made of Al, Sn, or In.

Borosilicate glass is used for the lower second substrate to be bonded to the lower surface of the first substrate 1, and the vibration chamber 9 is formed by bonding the second substrate 2 to the second substrate.
Gold is sputtered by 0.1 μm on each position corresponding to the vibration plate 5 on the substrate 2, and a gold pattern is formed in substantially the same shape as the vibration plate 5 to form the individual electrodes 21. Individual electrode 2
1 has a lead portion 22 and a terminal portion 23. Further, the Pyrex (registered trademark) sputtered film is covered by 0.2 μm on the entire surface except the electrode terminal portion 23 to form an insulating layer 24, and a film is formed to prevent dielectric breakdown, short circuit or the like when the inkjet head is driven. ing.

The insulating layer 24 does not necessarily have to be provided on the individual electrode 21. For example, a silicon oxide film (SiO ₂ ) may be formed on the entire surface of the first substrate 1 to serve as an insulating film. In this case, when an oxide film is formed on the common electrode portion, the contact portion has a MOS structure to form a capacitor. Therefore, it is preferable not to form an oxide film on the common electrode portion.

Further, the vibration chamber 9 provided in the first substrate 1
However, it is not always necessary to provide the vibration chamber 9 on the first substrate 1, as will be described later (FIG. 8).
Alternatively, the surface of the first substrate 1 to be joined to the second substrate 2 may be formed flat, a recess may be formed at a predetermined depth on the side of the second substrate, and a vibration chamber may be provided.

The upper third substrate 3 bonded to the upper surface of the first substrate 1 is made of borosilicate glass, like the second substrate 2. By joining the third substrate 3, the nozzle hole 4, the ejection chamber 6, the orifice 7, and the ink cavity 8 are formed. Further, the third substrate 3 is provided with an ink supply port 31 communicating with the ink cavity 8. The ink supply port 31 is connected to an ink tank (not shown) via a connection pipe 32 and a tube 33.

Next, the first substrate 1 and the second substrate 2 are anodically bonded by applying a temperature of 300 to 500 ° C. and a voltage of 500 to 800 V, and the first substrate 1 and the third substrate 3 under the same conditions. And the ink jet head is assembled as shown in FIG. After the anodic bonding, the gap length G formed between the diaphragm 5 and the individual electrode 21 on the second substrate 2 is equal to the recess 15
And the thickness of the individual electrode 21, which is 0.5 μm in this embodiment. In addition, the diaphragm 5 and the individual electrode 2
The gap G1 with the insulating layer 24 on the first layer is 0.3 μm.

After the ink jet head is assembled as described above, the common electrode 17 and the terminal portion 23 of the individual electrode 21 are formed.
A drive circuit 102 is connected between the wirings 101 to form an inkjet printer. Electrical connection between these electrodes 17 and 23 and the wiring 101 is performed by a method such as a brazing connection, an anisotropic conductive film formation and thermocompression bonding, or a conductive adhesive. For these connection methods, brazing is preferable in terms of mechanical strength and low contact resistance, but head multiple nozzles and high density,
From the viewpoint of miniaturization, the method using an anisotropic conductive film is most preferable. The ink 103 is supplied from the ink tank (not shown) to the inside of the first substrate 1 through the ink supply port 31, and fills the ink cavity 8, the ejection chamber 6, and the like.
The ink in the ejection chamber 6 is, as shown in FIG.
When the inkjet head 10 is driven, the ink droplets 104 are ejected from the nozzle holes 4 to be printed on the recording paper 105.

Next, the electrical connection of the ink jet head constructed as described above will be described in detail.

When the semiconductor and the metal in the electrode portion come into contact with each other with a boundary surface, depending on the type of the semiconductor and the metal,
A so-called rectifying contact (diode) is formed in which the electric resistance varies depending on the polarity of the voltage applied to the contact portion. Whether a rectifying contact or an ohmic contact whose electric resistance does not differ depending on the polarity of the voltage applied to the contact is formed is affected by the magnitude relationship of the work functions of metal and semiconductor. When the semiconductor substrate is a p-type semiconductor When the work function of a metal is larger than that of a semiconductor, ohmic contact is formed at the contact portion, and rectification contact tends to be formed in the opposite case, and an n-type semiconductor shows a property opposite to that of a p-type semiconductor. I know that.

FIG. 4 is a detailed partial cross-sectional view of the common electrode portion in this embodiment. FIG. 4A shows a structure in which the common electrode 17 is formed on the p-type silicon substrate 1p in which the whole silicon is doped with boron at a predetermined concentration in the first substrate 1, and FIG. 4B shows the whole silicon. A common electrode 17 is formed on an n-type silicon substrate 1n doped with, for example, phosphorus at a predetermined concentration, 17b and 17d are first layers made of Cr or Ti, and 17a and 17c are Au, Rh or Pt. 2 is a second layer of the insulating film and 19 is an insulating layer of an oxide film formed on the first substrate 1 except for the surface on which the common electrode 17 is formed.

If the semiconductor substrate is a p-type semiconductor, A
For the metal of u, Rh, and Pt, ohmic contact is formed at the contact portion for the reason described above, but rectifying contact is formed for Cr and Ti. Therefore, it is desirable to directly contact the metal of Au, Rh, and Pt with the semiconductor substrate, but these metals have poor adhesion to the semiconductor such as Si and cannot maintain sufficient mechanical strength as an electrode. On the other hand, Cr and Ti have good adhesion to semiconductors such as Si and metals such as Au, Rh, and Pt, and are therefore used as a semiconductor substrate and an intermediate layer between these metals. Shows the property as a rectifying contact. Therefore, as shown in FIG.
Forming the first layer 17b as a thin film having a thickness of 50 to 150Å level on the p-type semiconductor substrate, and forming the second layer 17a as a metal film having a thickness of 1000Å level on the first layer 17b. Thus, the influence of the rectifying contact caused by the contact between the first layer 17b made of Cr or Ti and the semiconductor substrate 1 is reduced as much as possible. As shown in FIG. 4A, when the thickness of the first layer 17b made of Cr and Ti is 50 to 150Å, the first layer is not uniformly uniform and many small holes 18 are formed. The resulting so-called porous state is formed, and the structure of the first layer 17a enters into this portion to form an ohmic contact. Therefore, if the thickness of the first layer 17b is 50 to 150Å, it is possible to maintain sufficient mechanical strength as an electrode and obtain sufficient ohmic contact.

On the other hand, when the semiconductor substrate is an n-type semiconductor, the metal of Au, Rh, and Pt forms a rectifying contact at the contact portion and the ohmic contact of Cr and Ti for the above-mentioned reason. In this case, as shown in FIG. 4B, when the thickness of the first layer is set to 300 Å or more, the small hole 18 shown in FIG. 4A does not occur, and the n-type semiconductor substrate 1n is made of Cr, Ti.
It is possible to form an ohmic contact with the first layer 17d consisting of, to maintain sufficient mechanical strength as an electrode, and to obtain a sufficient ohmic contact.

FIG. 4C shows a common electrode 17 of the p-type silicon substrate 1p in the electrode having the structure shown in FIG.
It is an electrode in which a high-concentration layer 17e of boron is formed by doping high-concentration boron (B) on the surface on which is formed. High concentration layer 1
Since the surface barrier formed between 7e and the common electrode is a thin potential barrier, a good ohmic electrode can be formed because charges freely pass by the tunnel effect. Also in the electrode having the structure shown in FIG. 4B, the same effect can be obtained by doping the surface forming the common electrode 17 with a high concentration of phosphorus (P).

FIG. 5 is a detailed partial cross-sectional view of a common electrode portion of another embodiment in this embodiment. The common electrode 17 includes an insulating film 19 formed on the entire surface of the semiconductor substrate 1.
Al or S on the part that was partially removed to attach
About 1000 Å of n or In is vapor-deposited, heated and thermally diffused to permeate these metals into the semiconductor substrate 1. Therefore, the contact portion 1 between the common electrode 17 and the semiconductor substrate 1
7f does not have a clear boundary surface like the common electrode of the two layers described above, and has a continuous connection structure in which the concentration of Al, Sn, or In gradually changes, and thus an ohmic connection can be obtained. In this case, Al and In can be applied to the p-type semiconductor substrate 1, and Sn can be applied to both the p-type and n-type semiconductor substrates 1.

In order to function as a terminal for connecting the drive circuit, the surface of the single-layer electrode made of Al is easily oxidized, and an insulating layer is easily formed on the surface, so that the second layer 17a described above is formed. , 17c is preferably a two-layered electrode using Au, Rh, and Pt metals.

Next, the influence on the driving of the ink jet head that occurs when resistance and capacitance are formed in the contact between the common electrode 17 and the semiconductor substrate 1 will be described.

FIG. 6A is an equivalent circuit diagram when a plurality of diaphragms 5 are driven when resistance and capacitance are not added in the contact between the common electrode 17 and the semiconductor substrate 1.
(B) is an equivalent circuit diagram when a plurality of diaphragms 5 are driven when a capacitance is added at the contact between the common electrode 17 and the semiconductor substrate 1.

Here, Ca is each vibrating plate 5 and individual electrode 2.
The actuator formed by 1 functions as a variable capacitor because its distance changes during driving. Ccom is a capacitor generated by forming the above-mentioned depletion layer without forming ohmic contact at the connection between the semiconductor substrate 1 and the common electrode 17, and Vcom
h is a power supply voltage applied to the inkjet head, and is V
a is a voltage applied to each actuator, and Cco
When m does not exist (a), Vh becomes equal to Va.

When Ccom exists (b), the voltage Va applied to each actuator is represented by the following equation. Va = Vh.Ccom / (nCa + Ccom) ... [Formula 1] Here, n is the number of drive nozzles. Common electrode capacitance C
com is smaller than the actuator capacitance Ca, the drive voltage Va actually applied to each actuator.
Becomes smaller in inverse proportion to the number of drive nozzles. Therefore, the ink ejection speed becomes slower in inverse proportion to the number of driving nozzles, and each of the actuators arranged in parallel affects each other to cause a crosstalk that adversely affects the ink ejection.

FIG. 7 is a graph showing the result of calculating the relationship between the ink discharge speed Vm and the drive nozzle n based on the equation 1 by obtaining the drive voltage and the ink discharge speed as an experimental result. Here, Ccom is 608.2 pF and Ca is 277 pF, both values are calculated based on the measured values, and the inkjet head used for the measurement and the calculation is based on the intentional addition of capacitance to the common electrode portion. I am trying. In addition, the driving voltage Vh is assumed to be 35V and 45V.

When the ink discharge speed Vm is small, the amount of ink discharged per time also decreases in proportion to the ink discharge speed Vm, and therefore the dot diameter on the recording paper becomes small and the density of the entire recorded image becomes insufficient, I get the impression that the so-called contrast is poor. Ink droplets do not fly as one spherical droplet and fly as if a plurality of spherical droplets pull a string. Therefore, when the ink ejection speed Vm is low, liquid droplets other than the liquid droplet at the tip (hereinafter referred to as satellites) arrive at the recording paper with a delay, the dot diameter on the recording paper is deformed, and the sharp blurring from the entire recorded image occurs. I get the impression that it lacks. Further, when the scanning speed of the head 10 is increased, this tendency becomes more remarkable. Therefore, in view of improving the printing speed, it is inconvenient that the ink discharge speed Vm is small, and the ink discharge speed of 10 m / sec or more is preferable. Is desired to be obtained.

As shown in FIG. 7, when the additional capacitance appears in the common electrode portion, the ink ejection speed becomes slow in inverse proportion to the number of driving nozzles, and good print quality cannot be expected in a multi-nozzle inkjet head. .

The case where a capacitance is generated at the connecting portion between the semiconductor substrate 1 and the common electrode 17 has been described above.
Even when a resistance is generated in the same portion, the phenomenon that the ink ejection speed decreases similarly depending on the number of drive nozzles occurs, which is a problem.

Next, the method for manufacturing an ink jet head of the present invention will be described in more detail based on the following examples.

FIG. 8 is a sectional view of the final shape of the ink jet head obtained by the manufacturing method of this embodiment.

As shown in FIG. 8, the ink jet head of this embodiment has a first substrate 1 having nozzles 4 for ejecting ink, a pressure chamber 6 for pressurizing the ink, a vibrating plate 5, a common electrode 17 and the like. And a second substrate 2 on which the individual electrodes 21 are formed and a third substrate 3 are laminated.

The first substrate 1 is a p-type single crystal Si substrate having a crystal plane orientation of (100), and has a nozzle 4 and a diaphragm 5.
Are formed by etching away unnecessary portions of the Si substrate. In this example, the nozzle and the diaphragm were formed by anisotropic etching of Si with an alkaline solution. As is well known, when single crystal Si is etched with an aqueous solution of potassium hydroxide or an alkali such as hydrazine, the difference in etching rate between crystal planes is large, so that anisotropic etching is possible. Specifically, since the etching rate of the (111) crystal plane is the smallest, a structure in which the (111) plane remains as a smooth surface is obtained as the etching progresses.

The manufacturing process of the first substrate 1 will be described with reference to FIG. An SiO ₂ film 19, which is an etching resistant material, is formed on both surfaces of a 200 μm thick Si substrate 1a (p type semiconductor substrate having a resistivity of 20 Ω · cm) by thermal oxidation to a thickness of 1 μm (FIG. 9A). ). Then, the SiO
On ₂ film 19, a photoresist pattern (not shown) corresponding to the shape of a nozzle 4 and the pressure chamber 6, to remove an unnecessary portion of the SiO ₂ film 19 by hydrofluoric acid etching solution (Fig. 9 ( b)). Next, Si was etched using a potassium hydroxide aqueous solution containing isopropyl alcohol. As described above, the (111) plane appears in the etched portion of Si, and its size is proportional to the etching depth. In the etched portion of the nozzle 4, the (111) planes appearing from both sides finally intersect with each other, and further etching hardly progresses. That is, the nozzle 4 has a sectional shape that is uniquely determined by the dimensions of the photoresist pattern corresponding to the nozzle 4.

On the other hand, the diaphragm 5 also has a shape determined by the size of the portion of the photoresist pattern corresponding to the diaphragm 5. In this case, the surface of the diaphragm 5 is the Si substrate 1a. The dimensions are designed so that it is the same (100) plane as the surface of. In this example, the thickness of the diaphragm 5 was determined to be 30 microns and the width thereof was determined to be 500 microns due to the ejection characteristics of the inkjet head. Si single crystal (100)
Since the plane and the (111) plane intersect at 54.7 degrees, the dimension of the photoresist pattern corresponding to the diaphragm 5 is set to 730 μm in width. In the etching process, the Si substrate 1a is etched by 170 microns,
The SiO ₂ film 19 which is the etching resistant mask is completely removed to obtain the nozzle 4 and the diaphragm 5 having a desired shape (FIG. 9).
(C)).

Next, the common electrode 17 is formed. Si substrate 1
A photoresist pattern (not shown) in which a void corresponds to the shape of the common electrode 17 is formed on a, and a two-layer film (Cr: Au) made of Cr and Au is formed on the photoresist pattern by using a sputtering device. 0.01 micron, Au:
0.1 micron), then the Si substrate 1a is immersed in acetone, and ultrasonic vibration is applied to the photoresist pattern and only the portion deposited on the photoresist pattern of the Cr—Au 2 layer film. Is removed and the two-layer film is used as the common electrode 17 (FIG. 9D).

As a method of forming the common electrode 17, in addition to the above method, a method of directly forming a Cr-Au two-layer film on the Si substrate 1a and then removing an unnecessary portion of the Cr-Au two-layer film by selective etching is also available. is there.

The first substrate 1 is formed through the above steps.

Next, the manufacturing process of the second substrate 2 will be described with reference to FIG. On the borosilicate glass substrate 2a, the vibrating plate 5 and the individual electrodes 2 arranged to face the vibrating plate 5 are arranged.
1 and a photoresist pattern (not shown) corresponding to the shape of the gap portion 83 between them is formed, and then a Cr—Au two-layer film 85 is formed by a sputtering method, and then the glass substrate 2a is immersed in acetone. Then, ultrasonic vibration is applied to the photoresist pattern and the Cr-Au bilayer film 85.
Only the portion deposited on the photoresist pattern is removed, and the remaining Cr—Au 2 layer film 85 is removed by the gap 8
3 is used as an etching mask for forming by etching (FIG. 10A).

Then, the glass substrate 2a is etched with a hydrofluoric acid-based etching solution to form a gap portion 13 having a depth of 0.35 μm, and the etching mask Cr-Au is used.
The two-layer film 85 is removed with aqua regia (FIG. 10 (b)).

Subsequently, on the glass substrate 2a, a photoresist pattern (not shown) whose voids correspond to the shape of the individual electrodes 21 is formed, and then an Al film having a thickness of 0.15 micron is formed by a vacuum evaporation method. Is formed on a photoresist pattern, and then the glass substrate 2a is immersed in acetone and ultrasonic vibration is applied to remove only the photoresist pattern and the Al film deposited on the photoresist pattern. The formed Al film is used as the individual electrode 21 (FIG. 10C).

Finally, the glass substrate 2a is formed by the sputtering method.
The borosilicate glass thin film 2 is provided at a location corresponding to the upper diaphragm 5.
4 as a protective film to obtain the second substrate 2 (FIG. 10).
(D)).

Through the above steps, the manufactured first substrate 1 and second substrate 2 are bonded by the anodic bonding method. The joining process is as follows. First, the Si substrate 1a and the glass substrate 2a are washed and dried, then the corresponding patterns of the Si substrate 1a and the glass substrate 2a are aligned with each other, and the both substrates are superposed. Next, both substrates were heated to 300 degrees Celsius on a hot plate, and a DC voltage of 500 V was applied for 10 minutes with the Si substrate 1a side being positive and the glass substrate 2a side being negative to perform bonding.

Next, the Si substrate 1a and the third substrate 3 are joined. In this embodiment, the third substrate 3
Is a borosilicate glass like the second substrate 2, and the joining method was the anodic joining method described above.

Hereinafter, the results of a printing test performed by connecting the drive circuit 102 to the common electrode 17 and each individual electrode 21 of the ink jet head formed by a series of steps of this embodiment will be described.

FIG. 11 is a diagram showing the configuration of the drive circuit 102 of the ink jet head. The drive circuit 102 is composed of transistors 41, 42, 44, 45, etc. as shown in the figure. Transistor 4 in standby state
Both 2 and 45 are turned off, and the terminal voltage Vh is not applied to the capacitor Ca composed of the diaphragm 5 and the individual electrode 21. Therefore, the drive voltage is not applied to the diaphragm 5-the individual electrode 21. . Therefore, the vibrating plate 5 is not displaced and no pressure is applied to the ink in the ejection chamber 6. Next, when the charging signal 51 is turned on, the transistor 41 is turned on at the rising edge of the signal and the transistor 4 is turned on.
Since 2 also turns on, the terminal voltage Vh is applied to the capacitor Ca, and thereby the drive voltage Va (Va = Vh) is applied between the diaphragm 5 and the individual electrode 21. Therefore, the arrow A
Current flows in the direction, and as described above, the diaphragm 5 -the individual electrode 2
The vibrating plate 5 is attracted to the individual electrode 21 side and bends by the electrostatic force acting between the two due to the electric charge charged between the two. As a result, the volume of the ejection chamber 6 increases and ink is sucked.

Next, when the charge signal 51 is turned off and the discharge signal 52 is turned on, the transistors 41 and 42 are turned off, so that the charging of the capacitor Ca is stopped, whereby the charge between the diaphragm 5 and the individual electrode 21 is charged. Will stop. On the other hand, transistor 44 is turned off, which causes transistor 45.
Also turns on. When the transistor 45 is turned on, the electric charge accumulated in the capacitor Ca (between the vibration plate 5 and the individual electrode 21) is discharged in the direction of arrow B through the resistor 46. In the figure, the resistor 46 is set to be considerably smaller than the resistor 43 and has a small time constant at the time of discharging, so that the resistor 46 is discharged in a time sufficiently shorter than the charging time. At this time, the vibrating plate 5 is released from the electrostatic force all at once, and returns to the standby position due to the rigidity of the vibrating plate 5 itself, suddenly presses the ejection chamber 6, and the pressure generated in the ejection chamber 6 causes the ink droplet 104 to be ejected into the nozzle hole. Discharge from 4. In this embodiment, it is assumed that the first substrate 1 is a P-type semiconductor substrate, but when an N-type semiconductor substrate is used as the substrate, the connection wiring between the drive circuit 102 and the inkjet head 10 is connected. Must be opposite to the case of P-type semiconductor.

FIG. 12 shows the ink jet head 10 described above.
FIG. 2 is a schematic diagram of a printer equipped with the. 300 is recording paper 1
A platen 301 for transporting 05 is an ink tank for storing ink therein, and supplies ink to the inkjet head 10 via an ink supply tube 306.
Reference numeral 302 denotes a carriage, which is the inkjet head 10.
Is moved in a direction orthogonal to the conveyance direction of the recording paper 105. Reference numeral 303 denotes a pump, which is the inkjet head 10.
In the case of defective ink ejection, etc., it has a function of sucking the ink through the cap 304 and the waste ink collection tube 308 and collecting it in the waste ink reservoir 305.

When a driving experiment was conducted at a driving voltage of 40 V using the circuit of FIG. 11 and the printer shown in FIG. 12, the frequency characteristics of the ink droplet ejection speed and the ink droplet volume were 7 ± 0.3 m / up to 8 kHz, respectively. Seconds and 0.1 ± 0.0
It was in the range of 2 × 10 ⁻⁶ ml / dot, flat characteristics were obtained up to high frequencies, and it became clear that it is suitable for high-speed printing.

In this embodiment, Cr- is used as the common electrode 17.
An Au two-layer film was used, but in addition to this, a Ti-Pt two-layer film,
The same effect can be obtained by using a metal such as a Ti-Rh two-layer film that can make ohmic contact with the p-type Si substrate. Also, the first
When an n-type Si substrate is used as the substrate of
The same effect can be obtained by using a metal such as Sn that can make ohmic contact with the mold Si substrate.

Next, with respect to the ink jet head of this embodiment, an experiment was conducted on the effect of the resistance component contained in the drive circuit on the drive of the ink jet head.

FIG. 13 is an equivalent circuit diagram of the drive circuit in the experiment. Rsi is the resistance value of the silicon substrate 1 itself, the resistance value is equivalent to 20 Ω · cm, Ca is the diaphragm 5 and the individual electrode. 21 is a capacitor having a capacitance of about 300 pF when the diaphragm 5 is not attracted to the individual electrode 21. Rc is a resistance provided in the drive circuit, and this time, a comparative experiment was performed with resistance values of 1 kΩ and 10 kΩ. An experiment was conducted by fixing the drive voltage Vh to 35 V and inputting a signal having a drive frequency of 3 kHz to the signal input terminal P.

FIG. 14 is a graph showing a waveform obtained by observing the drive waveform of Vo of the drive circuit of FIG. 13 with an oscilloscope. A waveform 91 is a drive waveform when the circuit resistance Rc is 1 kΩ, and a waveform 92 is a drive waveform when the circuit resistance Rc is 10 kΩ. The waveform 92 has a larger time constant than the waveform 91, and the ink jet head driven by the waveform 92 cannot obtain a sufficient ink ejection speed in all the nozzles. On the other hand, in the ink jet head driven by the waveform 91, an ink ejection speed of 10 m / sec or more was obtained with almost all the nozzles. It is considered that this difference occurs because the diaphragm 5 cannot be sufficiently attracted to the individual electrode 21 due to the large time constant, but in any case, the resistance component connected in series to the capacitor Ca is used. Was found to greatly affect the inkjet head drive characteristics.

Therefore, in the case of the ink jet head obtained in this example, the resistivity of the silicon substrate was 20 Ω · cm.
If it is not more than about 10 Ω · cm, sufficient ink discharging performance can be obtained, but if it is about 30 Ω · cm, sufficient discharging performance cannot be obtained, and it is necessary to suppress the resistivity to 20 Ω · cm or less. It is preferable that the diameter is smaller than cm because the ink ejection characteristics are extended to the high frequency side.

Next, the manufacturing method of the particularly high resolution ink jet head of the present invention will be described in more detail based on the following examples.

FIG. 15 is a sectional view of an ink jet head according to another embodiment of the present invention. In the present invention, the inkjet head has basically the same structure as the inkjet head of the embodiment shown in FIG. 8, except that the first substrate 1b on which the nozzles 4a and the pressure chambers 6a are formed has a crystal structure. The distance between adjacent pressure chambers is minimized by using a single crystal Si substrate whose plane is the (110) plane.
A high-density inkjet head is being formed by using a Si substrate having a resistivity of m as the first substrate 1b.

In the (110) Si substrate, the (111) plane intersects the substrate surface perpendicularly, and the shape of the pressure chamber 6a is surrounded by a wall perpendicular to the substrate surface as shown in FIG. By adopting the structure, the structure in which the distance between the adjacent pressure chambers is minimum, that is, the structure with the highest density can be obtained.

In this embodiment, the pitch between the pressure chamber and the nozzle is 70 microns, that is, 360 dpi (dots per inch), and the width of the pressure chamber 6a is 50 microns. In the structure of the inkjet head according to the present embodiment, the width of the pressure chamber 6a and the width of the diaphragm 5a are the same. From the vibration characteristics of a thin plate with a width of 50 microns, the vibration plate 5a
The optimum thickness is 1 micron. There are several possible methods for forming a 1 micron thin plate, but in this embodiment, the surface of the Si substrate on which the thin plate is formed has a boron concentration of 1 × 10 ²⁰ pieces / cm ³ at a depth of 1 micron. I adopted the method of doping. When etching Si with an alkali, the etching rate becomes very slow at the above-mentioned high boron concentration, so that a structure in which only the 1-micron-thick boron-doped layer remains can be obtained.

The nozzle 4a is also formed by anisotropic etching with alkali.

The common electrode 17 is formed similarly to the ink jet head of the embodiment shown in FIG. 8, and the second substrate and the third substrate are formed similarly to the ink jet head of the embodiment shown in FIG. Then, an inkjet head was formed by the same process.

When a driving test was conducted at a driving voltage of 40 V using the circuit of FIG. 11 and the printer shown in FIG. 12, the frequency characteristics of the ink droplet ejection speed and the ink droplet volume were 10 ± 0.4 m / 9 up to 9 kHz, respectively. Seconds and 0.1 ± 0.
In the range of 01 × 10 ⁻⁶ ml / dot, flat characteristics up to high frequencies were obtained, and a high-speed, high-density inkjet head was obtained.

When designing such a high resolution ink jet, the resistance value of the semiconductor substrate becomes a problem.

For example, (10 of the Si substrate shown in FIG.
0) surface of the embodiment of the manufacturing method of the inkjet head is premised, a low-resolution inkjet head of about 40dpi is designed, and the embodiment using the (110) surface of the Si substrate shown in FIG. Taking the case of designing an inkjet head having a medium resolution of about 180 dpi as an example on the assumption of an inkjet head manufacturing method, an inkjet head of about 180 dpi has an ink flow path formed by etching, and then discharges remaining on the Si substrate. The cross-sectional area of the peripheral wall of the chamber 6 and the vibration plate is 40
This is about 1/10 of the cross-sectional area of the inkjet head of about dpi, and accordingly, the resistance Rsi between the common electrode 17 and the diaphragm 5 is substantially about 10 times. On the other hand, since the area of the individual electrode 21 is ½, the capacity of the capacitor Ca including the diaphragm 5 and the individual electrode 21 is also ½. Therefore, when the Si substrate having the same resistivity is used as the first substrate 1, the time constant Rsi · Ca of the medium resolution inkjet head of about 180 dpi is 5 times the time constant of the low resolution inkjet head of about 40 dpi. Become.

Therefore, depending on the resolution, the first substrate 1
It is necessary to properly select the resistivity of.

Next, another method of manufacturing the ink jet head of the present invention will be described in more detail based on the following examples.

In the ink jet head of this embodiment,
A p-type Si substrate is used as the first substrate, and the portion of the Si substrate where the common electrode is formed is doped with high concentration boron.

As described above, in the ink jet head driving method of the present invention, since the vibration plate 5 is deformed by static electricity between the vibration plate 5 and the individual electrode 21 arranged facing the vibration plate 5, the high speed of the ink jet head. In this case, it is essential to speed up the supply of electric charges to the diaphragm 5. That is, the drive circuit 102 and the Si substrate, which is a support substrate of the diaphragm 5 and is also a path for electric charges, must be connected so that the contact resistance is as small as possible and the diode characteristics are not present. The use of the common electrode material that makes ohmic contact with the Si substrate, such as the inkjet head of the embodiment shown in FIG. 8, satisfies the above requirements, but when the inkjet head is required to achieve higher speed, It is considered that the contact portion of the Si substrate with the drive circuit 102 is doped with impurities to reduce the resistance.

In this embodiment, boron ions are implanted on the surface of the Si substrate, which is the first substrate of the ink jet head of the embodiment shown in FIG. 15, on which the common electrode 7a is formed. The conditions for ion implantation are as follows.

The ion acceleration voltage was 120 keV, the doping amount was 5 × 10 ¹⁶ ions / cm ² , and the post-implantation annealing treatment was performed at 1000 ° C. for 1 hour, and the volume concentration of boron on the surface of the Si substrate was 5 × 10 5. It became ¹⁹ pieces / cm ³ . Then, the steps after the formation of the common electrode were performed in the same manner as in the case of the inkjet head of the embodiment shown in FIG. 15, to manufacture an inkjet head.

When the actual print test of the ink jet head obtained in this example was conducted at a driving voltage of 40 V using the circuit of FIG. 11 and the printer shown in FIG. 12, the ink drop ejection speed and the ink drop volume were confirmed. The frequency characteristics are 10 ± 0.4 m / sec and 0.1 ± up to 12 kHz, respectively.
In the range of 0.01 × 10 ⁻⁶ ml / dot, flat characteristics were obtained up to high frequencies, and a high-speed and high-density inkjet head was obtained.

In this example, the volume concentration of boron in the boron-doped portion of the Si substrate was 5 × 10 ¹⁹ pieces / cm ³ , but in principle, the volume concentration of boron in the doped portion is 10 ¹⁹ or more. The resistance value becomes very small, and the same effect can be obtained. When an n-type Si substrate is used as the first substrate, similar effects can be obtained by similarly doping the impurities of the V group element.

Further, another mode of the common electrode of the ink jet head of the present invention will be described based on the following examples.

FIG. 16 shows a plan view of an ink jet head of another embodiment according to the present invention.

The common electrode 17 made of the two-layered Cr-Au metal film is provided at the rear of the common ink chamber 8 and has the purpose of expanding the contact area with the silicon substrate 1 as much as possible and reducing the connection resistance. To minimize the distance of silicon between the common electrode 17 and the
In order to make the speed of the ink droplets ejected from and the ink ejection amount uniform, they are provided so as to be wide in the direction in which the ejection chambers 6 are arranged and the distances between the respective vibration plates 5 and the common electrode 17 are equal. There is.

According to this embodiment, since the distance from the common electrode 17 to each diaphragm 5 is equal, each diaphragm 5 at the time of driving.
Since the resistance value between the common electrodes can be made uniform, it is possible to prevent the ink ejection characteristics of the nozzles 4 from becoming non-uniform due to the non-uniform resistance value.

Next, another mode of the common electrode of the ink jet head of the present invention will be described based on the following examples.

FIG. 17 shows a sectional view of an ink jet head of another embodiment of the present invention.

The common electrode 17 is formed with the above-mentioned two-layered Cr-Au metal coating film up to the upper surface of the diaphragm 5. The common electrode 17 is in contact with the ink, but the common electrode 17 will not be galvanically corroded if the entire ink is set to an equipotential. According to the present embodiment, the common electrode 17 and the first substrate 1
Since it is possible to form a larger contact area with and to minimize the movement distance of charges in the first substrate 1, it is possible to reduce the electric resistance value as a whole. In particular, it is effective when the inkjet head is required to be downsized and the common electrode cannot be sufficiently obtained.

Although silicon has been mainly described as the semiconductor of the first substrate 1 in each of the embodiments, semiconductors other than silicon may be used as the material of the first substrate, such as germanium (Ge) and gallium arsenide (GaAs). ) And indium tin (InSn), the same action and effect can be obtained. Particularly when Ge is used, the impurity concentration can be easily controlled and a substrate having a uniform resistance value can be produced.

[0093]

As described above, the ink jet head of the present invention is suitable for the recording means of the ink jet recording apparatus,
It is particularly suitable as a recording means for a small printer that can be efficiently driven with a low power supply voltage and is expected to have high printing speed and high printing quality.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a cross-sectional side view of the entire inkjet head shown in FIG.

FIG. 3 is a view taken along the line AA of FIG.

FIG. 4 is a detailed partial cross-sectional view of a common electrode portion in the embodiment.

FIG. 5 is a detailed partial cross-sectional view of a common electrode portion according to another aspect of the embodiment.

FIG. 6 is an equivalent circuit diagram when an inkjet head is driven in consideration of contact between a common electrode and a semiconductor substrate.

FIG. 7 is a characteristic diagram showing a relationship between an ink ejection speed Vm and a drive nozzle n.

FIG. 8 is a sectional side view of an inkjet head according to another embodiment of the present invention.

FIG. 9 is a manufacturing process diagram of the substrate of the inkjet head in FIG.

FIG. 10 is a manufacturing process diagram of the substrate of the inkjet head in FIG.

FIG. 11 is a diagram showing a configuration of a control drive circuit of the embodiment.

FIG. 12 is a schematic diagram of a printer equipped with the inkjet head of the embodiment.

FIG. 13 is an equivalent circuit diagram of a drive circuit in a characteristic test of the inkjet head of the embodiment.

FIG. 14 is a characteristic diagram in which a drive waveform of the drive circuit is observed with an oscilloscope.

FIG. 15 is a side sectional view of an inkjet head according to another embodiment of the present invention.

FIG. 16 is a plan view of an inkjet head according to another embodiment of the present invention.

FIG. 17 is a side sectional view of an inkjet head according to another embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichi Yotsuya 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Co., Ltd. (72) Inventor Masahiro Fujii 3-3.5 Yamato, Suwa-shi, Nagano Sei Co-Epson Corporation (72) Inventor Naoki Kobayashi 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (8)

(57) [Claims] 1. A semiconductor substrate integrally formed with at least a part of a discharge chamber communicating with a nozzle and a diaphragm provided in a part of the discharge chamber, and an electrode facing the diaphragm with a gap. In the inkjet head that stacks the formed substrate, applies an electric pulse between the semiconductor substrate and the electrode, deforms the diaphragm by the generated electrostatic force, and ejects ink, the resistivity of the semiconductor substrate is: An inkjet head having a resistance of 20 Ω · cm or less. 2. A metal film formed of Cr or Ti for the first layer and Au, Rh, or Pt for the second layer is formed on a part or all of the surface of the semiconductor substrate other than the position facing the electrode. The inkjet head according to claim 1, wherein the inkjet head is provided. 3. Al, Sn, or I on a part or all of the surface of the semiconductor substrate other than the position facing the electrode.
The inkjet head according to claim 1, wherein a metal film made of n is formed. 4. The semiconductor substrate is a p-type semiconductor, and at least a portion of the surface of the semiconductor substrate where the metal film is formed is doped with a group III element. The inkjet head according to claim 3. 5. A group III element volume concentration of at least a portion of the surface of the semiconductor substrate where the metal film is formed is 10.
The inkjet head according to claim 4, wherein the number is ¹⁹ / cm ³ or more. 6. The semiconductor substrate according to claim 2, wherein the semiconductor substrate is an n-type semiconductor, and a group V element is doped at least on the surface of the semiconductor substrate where the metal film is formed. The inkjet head according to claim 3. 7. A group V element volume concentration of at least a portion of the surface of the semiconductor substrate where the metal film is formed is 10 ¹⁹
7. The inkjet head according to claim 6, wherein the number is not less than 1 / cm ³ . 8. The semiconductor substrate is formed with a plurality of the vibrating plates, and the metal film is formed at a position where respective distances from the respective vibrating plates to the metal film are equal to each other. The inkjet head according to any one of claims 2 to 7.