JPS5842834B2 - netinserthead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monolithic thermal printing head, and is particularly intended to provide a thermal printing head with high reliability and high heat generation efficiency.

Conventional monolithic thermal printing heads can be classified into the following three types depending on the position of the heating resistor layer in the thickness direction of the semiconductor substrate.

Namely, (a) a heat generating resistance layer such as a diffusion layer is placed on the side of the semiconductor substrate that does not come into contact with the thermal paper, and (b) a heat generating resistance layer such as a diffusion layer is placed on the side of the semiconductor substrate that comes into contact with the thermal paper. (C) Something that causes the collector saturation resistance to generate heat.
There are three.

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. When operated at 100°F, the temperature generally drops by 50°C or more, and the temperature of the semiconductor substrate rises to 50°C or more higher than the coloring temperature of thermal paper, which is disadvantageous in terms of heat utilization efficiency, and thermal printing This caused a decrease in the reliability of the head.

Next, since the thermal printing head in (b) only requires a wear-resistant layer between the heat-generating resistance layer and the thermal paper, the temperature of the semiconductor substrate only needs to rise to a level slightly higher than the coloring temperature of the thermal paper. Therefore, the heat utilization efficiency is high, but if cracks occur in the wear-resistant layer due to aging, there is a problem that the withstand voltage of the heat-generating resistor layer separated by the PN junction decreases, leakage current increases, etc., and reliability decreases.

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 a crack occurs in the wear-resistant layer, there is no PN junction 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 is the thermal printing head described in (b) above, but the heating resistance layer is not separated by a PN junction like in the past, and there is no PN junction on the side that contacts the thermal paper. This thermal printing head is highly reliable and suitable for high-speed operation.

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 0.5 QcfrL, thickness 300
Semiconductor substrate such as μm N-type silicon, 2 is 10 μm deep
m of P-type diffusion regions are formed so as 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 porous silicon layer 4 with a depth of about 10 μm as shown in FIG. Change.

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.

The porous silicon layer 4 has a very fast oxidation rate of 0° and 1
When oxidized for 1 hour in humid oxygen at 100° 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 and an emitter 8.

The surface of the silicon substrate 1 opposite to the surface on which the base 7 and emitter 8 are formed, that is, the back surface, is removed by lapping and etching to obtain a thickness of 50 μm as shown in FIG.

After selectively forming a deep N-type diffused layer 9 to serve as a collector contact at a position corresponding to the back surface of the emitter 8, an N-type diffused layer 10 shallower than the deep N-type diffused layer 9 is formed on the entire back surface.
form.

At this time, a thermal oxide film 11 is formed.

Next, holes are opened in the thermal oxide film 11 on the back surface to form a collector electrode 12, and holes are opened in the base 7 and emitter 8 on the front surface to form a base electrode 13 and an emitter electrode 14.

The silicon substrate 1 is selectively etched from a position corresponding to the back surface of the oxide layer 5 to form a mesa groove 15.

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 the depth of the mesa groove 15 is determined by the depth when the bottom surface of the oxide layer 5 is reached. This is convenient because it almost stops.

Finally, a wear-resistant layer 16 such as SiC is formed on the entire back surface.

A region surrounded by oxide layer 5 and mesa groove 15 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.

Note that if it is necessary to lead out the collector electrode 12 to the front side of the silicon substrate 10, various methods can be applied.

For example, a C.
The collector electrode may be led out to the surface of the silicon substrate 1 by forming a conductive layer using a thin film forming method with excellent throwing power, such as a VD method, a sputtering method, or a plating method.

As can be seen from FIG. 6, the operation of the thermal printing head of the present invention is such that electrons injected from the emitter 8 pass through the base 7 and the silicon substrate 1, reach the N-type diffusion layer 9, and form a shallow N-type diffusion layer. 10 and exits the electrode 12.

Some electrons directly reach the shallow N-type diffusion layer 10 from the silicon substrate 1 without passing through the N-type diffusion layer 9, but due to the specific resistance of the silicon substrate 1 and the sheet resistance of the shallow N-type diffusion layer 10, By selecting the distance between the emitter junction and the N-type diffusion layer 9, it is possible to cause most of the current to flow through the shallow N-type diffusion layer 10.

Therefore, since the main heat generating position of the thermal printing head of the present invention is the shallow N-type diffusion layer 10, it is close to the thermal paper and heat is effectively transferred, resulting in a thermal printing head with high thermal efficiency.

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

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 16 due to changes over time, problems such as deterioration of withstand voltage and increase in leakage current as in the case of a PN junction do not occur, so the thermal printing head is highly reliable.

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 present invention in the order of steps. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 7... Curved base, 8... Curved emitter, 9... Deep diffusion layer (collector contact), 10... Diffusion layer, 12... Tune collector electrode.

Claims (1)

[Claims] 1 An emitter and a base are provided on the surface of the semiconductor substrate that does not come into contact with the thermal paper, a diffusion layer of the same conductivity type as the emitter is provided on the surface that comes into contact with the thermal paper, one end of this diffusion layer acts as a collector contact, and the other end Deriving the electrode from
A thermal printing head characterized in that the diffusion layer between the collector contact and the electrode serves as a main heating resistor.