JPS63257652A - Substrate for thermal head - Google Patents

Abstract

PURPOSE:To obtain a thermal head having favorable thermal response characteristics and consuming less electric power, by providing a single-crystal silicon plate, a porous silicon oxide layer and a non-porous insulator layer provided on the silicon oxide layer. CONSTITUTION:This substrate for a thermal head comprises a single crystal silicon plate 1 having high thermal conductivity, a layer of porous silicon oxide 2 provided by subjecting a resistor-forming surface of the plate 1 to anodic electrolysis and then to thermal oxidation, and a non-porous insulator layer 3 provided on the layer of silicon oxide 2. The silicon oxide layer 2 has a film thickness of 5-100 mum and a porosity of 30-70%. The non-porous insulator layer 3 is a silicon oxide film provided by sputtering, which has a film thickness of 0.1-2 mum. The silicon oxide layer 2 has low thermal conductivity and thermal capacity, because of the presence of fine pores. The non-porous insulator layer 3, which functions to seal the pores present at the surface of the silicon oxide layer 2, can be provided in a small thickness because the pores are small in size. Therefore, the overall thermal conductivity and thermal capacity can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a substrate for a thermal head using single crystal silicon.

[Conventional technology]

Conventionally, a so-called glazed alumina substrate, which is an alumina substrate coated with glass, has been used as a thermal head substrate, and this is still the mainstream. However, in recent years, the power consumption of thermal heads has been reduced,
Due to the demand for high printing quality, a low temperature layer (equivalent to glaze)
It became necessary to reduce the thermal conductivity or heat capacity of the material, and to increase the thermal conductivity of the heat dissipation layer (equivalent to alumina).

In Japanese Unexamined Patent Publication No. 60-141569, the thermal conductivity and heat capacity are reduced by using multicellular glass as the heat insulating layer. Additionally, to improve yield, the surface on which the resistor film will be formed is coated with an insulating layer to smooth it.

[Problem that the invention seeks to solve]

However, the thermal head substrate with the above structure has a small porosity of 20 to 30% in the heat insulating layer and a smoothing layer of 1 to 10 μm on the heat insulating layer, so the thermal conductivity and heat capacity are sufficiently low. Therefore, there was a problem that the effect of reducing power consumption was small.

As stated above, it is an object of the present invention to provide a thermal head substrate that eliminates the problem that power consumption is not sufficiently reduced and provides high print quality with low power consumption.

(Means for Solving the Problems) The thermal head substrate of the present invention includes a single-crystal silicon plate and a resistor-forming surface of the single-crystal silicon plate subjected to electrolysis using hydrofluoric acid, followed by thermal oxidation. It has a porous silicon oxide layer formed by this method, and a nonporous insulating layer formed on the porous silicon oxide layer.

(Function) In the above configuration, since the porous silicon oxide layer has pores, its thermal conductivity and heat capacity are low.

In addition, the nonporous insulating layer on the porous silicon oxide layer has gaps that block the pores on the surface of the porous silicon oxide layer, but since the pore size of the porous silicon oxide layer is small, The non-porous insulating layer can be made thin. Therefore, these two
The overall thermal conductivity and heat capacity of the two layers can be reduced. Furthermore, single crystal silicon substrates have high thermal conductivity. Therefore, when a thermal head is formed using this substrate, a thermal head with good thermal response and low power consumption can be obtained.

(Embodiment) Fig. 1 shows a thermal head using a thermal head substrate according to an embodiment of the present invention. A silicon oxide (SiO2) film 3 is a non-porous insulating layer formed on the porous SiO2 film 2, for example, a SiO2 film.

4 is a TaN film as a resistor, and 5 is a Ni film as a conductor.
Cr-Au films 6 and 7 are a 5i02 film and a Ta205 film as protective films.

The silicon substrate 1 serves as a heat dissipation layer and has a thermal conductivity five times higher than that of conventionally used alumina.

The porous SiO2 film 2 has a porosity of about 50%, a thermal conductivity of 1/2 or less that of quartz glass, and a heat capacity of about 172 that of quartz glass, forming a good heat insulating layer. S
The iO2 film 3 is formed by sputtering, for example, and has a thickness of 1 μm or less, and seals the pores of the porous SiO2 film 2 without impairing the low heat capacity of the heat insulating layer.

Incidentally, instead of the non-porous SiO2 film 3, other materials such as Si3 N4, S! A film of O, Al103 may also be used.

An example of a method for manufacturing the above substrate will be described below.

First, the silicon substrate has a specific resistance of 0.01Ωc.
A P-type mirror substrate with m and (iii) planes is used.

Next, a 1Qwt% hydrofluoric acid (hydrofluoric acid) aqueous solution was placed in an electrolytic cell with the platinum plate as the cathode, and the above substrate was used as the anode to face the platinum plate, and electrolysis was carried out for 15 minutes at a current density of 50 mA/cm with direct current. do. This forms a porous silicon layer of approximately 50 μm. This thickness can be freely controlled by changing the electrolysis time.

Next, after thoroughly cleaning the above substrate, it is placed in a thermal oxidation furnace for 1
Thermal oxidation is carried out in dry oxygen at 000'C for 20 minutes.

This results in a porous silicon layer of 50 t1m, or 50 m of porous silicon layer.
It becomes porous SiO2@2 of μm. This porous SiO2
@2 has a pore size of about 100 to 300A. Next, a non-porous SiO2 film 3 having a thickness of 0.5μ771 is formed by RF sputtering.

As a result of the above, the pores of the porous SiO2 film 3 are made of non-porous SiO2.
A substrate having a structure sealed with two films 3 can be obtained.

An example of a method for forming a thermal head using the above substrate will be described below. The following example is a thin film 4 normal head.

First, Ta2N is formed as the resistor 4 by sputtering, and then N1cr-Au is deposited as the conductor 5. Next, the conductor 5 and the resistor 4 are etched simultaneously by photolithography. The conductor 5 on the heating resistor part is roughly etched away by photolithography to expose the resistor 4, and a @ structure is obtained in which the resistor is connected to the conductor 5 only on both sides (left and right ends in the drawing). . Next, a SiO2 film 6 and a Ta205 film 7 are formed as protective films by sputtering. This completes the thermal head. still,
The substrate of the above embodiment can also be used to form a thick film thermal head.

The thermal head formed as described above has the following characteristics.

(a) Due to the pores of the porous SiO2 film 2, the thermal conductivity and heat capacity are low.

(b) Since the pores of the porous SiO2 film 2 are small in size,
The thickness of the non-porous SiO2 film 3 can be reduced, and the heat capacity of the heat insulating layer can be reduced.

(c) Since the thermal conductivity of the silicon substrate 1 is high, the thermal responsiveness is good.

(iv) Since the thermal head is formed on the silicon substrate 1, it is possible to incorporate a driver IC, a matrix driving diode, etc. on the silicon substrate.

FIG. 2 shows the relationship between the porosity of the porous 5i02 film 2 and the printing energy by the thermal head. In A, the thickness of the nonporous SiO2 film 3 for sealing the pores is 2 μm, and in B, the thickness is 0.5 μm. In addition, porous SiO2
The film thicknesses of film 2 are A and B.

Both are 50 μm. From the same figure, high porosity and SiO2
It can be seen that printing energy decreases as the film 2 becomes thinner. The porosity of the porous 5102 membrane 2 can be changed by changing the electrolytic conditions during membrane formation.

The porous 5102 membrane 2 with a porosity exceeding about 70% has low mechanical strength and is unsuitable for use in thermal heads. On the other hand, if the porosity is about 30% or less, the thermal conductivity and heat capacity are too high and the effects of the present invention cannot be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the porous silicon oxide layer and the nonporous insulating layer formed thereon reduce the overall thermal conductivity and heat capacity of these two layers. It is possible to obtain a thermal head that can be made smaller in size, has good thermal response, and consumes less power.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a thermal head equipped with a thermal head substrate according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between porosity and printing energy. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Porous silicon oxide layer, 3... Nonporous silicon oxide layer. -9 Column I National porosity (〃) Porosity graph Energy Figure 2

Claims (1)

[Claims] 1. A single-crystal silicon plate, and a porous material formed by anodic electrolyzing the resistor-forming surface of the single-crystal silicon plate with hydrofluoric acid, followed by thermal oxidation. A thermal head substrate comprising a silicon oxide layer and a nonporous insulating layer formed on the porous silicon oxide layer. 2. The thermal head substrate according to claim 1, wherein the silicon oxide layer has a thickness of 5 to 100 μm and a porosity of 30 to 70%. 3. The thermal head substrate according to claim 1, wherein the non-porous insulating layer is a silicon oxide film formed by sputtering. 4. The thermal head substrate according to claim 1 or 3, wherein the nonporous insulating layer has a thickness of 0.1 to 2 μm.