JPS5842835B2 - netinserthead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monolithic thermal printing head, and particularly aims to provide a thermal printing head with high reliability and high heat generation efficiency. The following three types are classified according to the position of the heat generating resistor layer in the thickness direction of the semiconductor substrate.

That is, (a) a semiconductor substrate in which a heat generating resistive layer such as a diffusion layer is arranged on the side of the semiconductor substrate that does not come into contact with the thermal paper, and (b) a semiconductor substrate.

There are three types: (C) one in which a heat generating resistance layer such as a diffusion layer is arranged on the side that contacts the thermal paper, and (C) one in which a collector saturation resistor generates heat.

The thickness of the semiconductor substrate is generally 50μ due to device manufacturing requirements.
m or more, and in the thermal printing head of (a), the temperature drops due to the thermal resistance of the semiconductor substrate before the heat generated in the heat generating layer reaches the thermal paper. In general, when operating at 50°C, the temperature will drop by 50°C or more, and the temperature of the semiconductor substrate will rise to 50°C or more higher than the coloring temperature of thermal paper, which is disadvantageous in terms of heat utilization efficiency. This caused a decrease in reliability.

Next, since the thermal printing head shown in (b) only has an abrasion resistant layer interposed between the heating resistance layer and the thermal paper, the temperature of the semiconductor substrate rises to a level slightly higher than the coloring temperature of the thermal paper. However, if cracks occur in the wear-resistant layer due to aging, the withstand voltage of the heat-generating resistor layer separated by the PN junction will decrease, leakage current will increase, etc., and reliability will decrease. there were.

Furthermore, since the collector saturation resistance of the thermal printing head in (c) extends over almost the entire thickness of the semiconductor substrate, almost the entire thickness of the semiconductor substrate generates heat, and the thermal resistance is as shown in (a).
, (b), and therefore the heat utilization efficiency is also between (a) and (b).

As for reliability, even if cracks occur in the wear-resistant layer, there is no PU bond on this surface, so there are no problems such as a decrease in breakdown voltage or an increase in leakage current, and the reliability is high.

The thermal printing head of the present invention brings the heat generating position of the thermal printing head (C) closer to the thermal paper side to lower thermal resistance, improve heat utilization efficiency, and provide a head suitable for high-speed driving. be.

Hereinafter, the present invention will be explained with reference to the drawings of one embodiment.

FIGS. 1 to 6 show an embodiment of the present invention in the order of steps, and show a cross section of one heating element.

In Figure 1, 1 is specific resistance 0.51; jcrn, thickness 300μ
m semiconductor substrate such as N-type silicon, 2 is 10 μm deep
A P-type diffusion region is formed to surround each heating element.

Next, a nitride film 3 is selectively formed in areas other than the P-type diffusion region 2, and then a metal electrode is formed on the entire surface opposite to the surface on which the nitride film 3 is formed and protected with wax. When anodization is carried out by keeping the silicon substrate 1 at an anode potential and the opposing platinum plate at a cathode potential, the P-type diffusion region 2 becomes a second
As shown in the figure, it changes into a porous silicon layer 4 with a depth of about 10 μm.

Since a reverse bias voltage will be applied to the N-type silicon substrate 1 and the P-type diffusion layer 2 during the anodization, it is desirable to use a constant current power supply.

Since the porous silicon layer 4 has a very fast oxidation rate, 11
When oxidized for 1 hour in humid oxygen at 00° C., it is oxidized to a depth of about 10 μm and changes to an oxide layer 5 as shown in FIG.

At this time, a thermal oxide film 6 is simultaneously formed on the entire surface.

Next, as shown in FIG. 4, holes are opened in the thermal oxide film 6 to form a base 7, an emitter 8. A collector contact 9 is formed.

The surface opposite to the transistor forming surface of the silicon substrate 1, that is, the back surface, is removed by lapping and etching to a thickness of 50 .mu.m as shown in FIG. 5, and an N-type diffusion layer 10 is formed on the entire surface of this etched surface.

Next, as shown in FIG. A metal wiring layer is formed by opening a hole in the base 7° collector contact 9, and a mesa groove 11 is formed by selectively etching the silicon substrate 1 from a position corresponding to the back side of the oxide layer 5.

When an HF-HNO3-CH5COOH-based etching solution is used, the etching rate for the oxide layer 5 is slower than the etching rate for the silicon substrate 1, so when the depth of the mesa groove 11 reaches the bottom of the oxide layer 5, This is convenient because it almost stops.

Finally, a wear-resistant layer 12 made of SiC or the like is formed on the entire back surface.

A region surrounded by oxide layer 5 and mesa groove 11 constitutes one heating element.

A thermal printing head generally has a plurality of heating elements arranged in a matrix or in a line.

Since the heating elements are thermally isolated by the heat insulating oxide layer and air, there is little heat leakage and clear printing is possible.

FIG. 7 shows a second embodiment of the present invention, which differs from the first embodiment shown in FIG. 6 by etching the back surface of the silicon substrate 1 to make it thinner. A deep N-type diffusion layer 1. OA and IOB are selectively formed, and an N+ type diffused layer shallower than IOA and 10B is provided on the entire back surface or between N native type diffusion layers 10A and 10B.

The collector contact is also connected to the emitter 8 as in the case of Fig. 6.
It is preferable to form a deeper collector contact 9A as shown in FIG. 7 instead of forming the collector contact at the same time.

In the thermal printing head of the present invention configured as described above, the collector saturation resistance of the transistor generates heat.

The collector saturation resistance can be thought of as approximately the following three resistances connected in series.

That is, there are three resistances: a vertical resistance at the bottom of the emitter 8, a vertical resistance at the bottom of the collector contact 9, and a lateral resistance between the emitter 8 and the collector contact 9.

The lateral resistance between the emitter 8 and the collector contact 9 consists of the parallel resistance of the N-type silicon substrate 1 and the N-type diffusion layer 10, but the resistance value of the N-type diffusion layer 10 is designed to be lower. Then, mainly the N-type diffusion layer 10 generates heat.

In the embodiment shown in FIG. 7, the resistance below the emitter 8 and the collector contact 9A can be made sufficiently small, so that the heat generation rate in the N-type diffusion layer 10 can be further increased.

Therefore, the heat generated inside the silicon substrate 1 is small, and the N-type diffusion layer 10 located closest to the thermal paper becomes the main heat generating location. This is the print head.

Furthermore, all of the PN junctions of the thermal printing head of the present invention are present on the surface that does not contact the thermal paper, so that the passivation of the PN junctions can be ensured to be complete.

There is only an N+N junction and no PN junction on the side that contacts the thermal paper.

Therefore, even if cracks occur in the wear-resistant layer 12 due to aging, problems such as deterioration of withstand voltage and increase in leakage current unlike in PN junctions do not occur, resulting in a highly reliable thermal printing head.

Note that even if the types of P and N are replaced in the above explanation, the gist of the present invention will not change.

Further, an epitaxial substrate can be used as the silicon substrate.

Furthermore, it goes without saying that thermal isolation between heating elements can be achieved by using only air insulation or only an oxide layer.

[Brief explanation of the drawing]

1 to 6 are cross-sectional views showing an embodiment of the thermal printing head of the present invention in the order of steps, and FIG. 7 is a cross-sectional view showing a second embodiment of the thermal printing head of the present invention. 1...Semiconductor substrate, 7...Base, 8
...Emitter, 9...Collector contact, 10...Diffusion layer.

Claims (1)

[Claims] 1. An emitter, a base, and a collector contact are provided on a first main surface of a semiconductor substrate that is a collector that does not come into contact with the thermal paper, and an emitter, a base, and a collector contact are provided on a second main surface of the substrate that is in contact with the thermal paper. A thermal printing head characterized in that a diffusion layer of the same conductivity type as a contact is provided, the diffusion layer constitutes a transistor contributing to collector saturation resistance, and the collector saturation resistance is configured to generate heat. 2. Claim No. 2 characterized in that the depth of the diffusion layer of the same conductivity type as the collector contact provided on the surface to be in contact with the thermal paper is deeper on the back surface portion facing the emitter and collector contacts. Thermal printing head according to item 1.