JPS5839072B2 - netinserthead - Google Patents

Description

[Detailed Description of the Invention] In general, thermal printing heads include monolithic type, thin film type,
Although thick film systems and the like have been developed, the present invention relates to a monolithic system, and particularly to a thermal printing head that is suitable for high-density thermal printing heads, has a high heat generation effect, and is highly reliable.

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

The thickness of the semiconductor substrate is generally 50μ due to device manufacturing requirements.
m or more, and in the thermal printing head (a) described above, the temperature drops due to the thermal resistance of the semiconductor substrate before the heat generated in the heating resistance layer reaches the thermal paper, and for example, the thermal printing head arranged in high density is slightly When operated at high speed, 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, in the thermal printing head of b, since the abrasion resistant layer is simply interposed between the heating 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. Although the utilization efficiency of the heat generating resistor layer is high, there is a problem in that when cracks occur in the wear-resistant layer due to aging, the withstand voltage of the heat-generating resistive layer separated by the PN junction deteriorates, resulting in a decrease in reliability.

Furthermore, since the collector saturation resistance of the thermal printing head 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 between ayb and heat utilization efficiency. It is in the middle of ayb.

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.

However, in the conventional structure, the collector contact is on the same plane as the emitter and the base, so it is not suitable for making a thermal printing head with a high-density matrix array for printing kanji characters, for example, because it cannot obtain enough collector current for coloring. Met.

The thermal printing head of the present invention moves the heat generating position of the thermal printing head in C above closer to the thermal paper side to lower thermal resistance and improve heat utilization efficiency. The present invention aims to provide a thermal printing head which can increase the emitter area by forming the emitter on a surface, can form a high-density matrix arrangement, and is suitable for high-speed movement.

1 to 6 show an embodiment of the present invention in the order of steps, and show a cross section of one of the heating elements arranged in a matrix or in a row.

In Fig. 1, 1 is the specific resistance IQcm, 300 μm thick P-
type silicon substrate, 2 is the specific resistance grown on this, o, 1ρ
■, P-type epitaxial silicon layer with a thickness of 25 μm, 3
Each heating element is formed in a P-type diffusion region with a depth of 30 .mu.m so as to embed it somewhere.

Next, a nitride film 4 is selectively formed on the surface other than the P+ type diffusion region 3, and then a metal electrode is formed on the entire back surface where the nitride film 4 is not formed and protected with wax. When anodizing is performed by keeping the substrate 1 at an anodic potential and the opposing platinum plate at a cathodic potential, the final diffusion region 3 becomes the second
As shown in the figure, it changes into a porous silicon layer 5 with a depth of about 30 μm.

Note that the nitride film 4 is removed.

Since the porous silicon layer 5 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 30 μm and changes to an oxide layer 6 as shown in FIG.

At this time, a thermal oxide film 7 is simultaneously formed on the entire surface.

Next, as shown in FIG. 4, holes are opened in the thermal oxide film 7 to form a base 8 and an emitter 9.

By lapping, polishing, and etching the back surface, the silicon substrate 1 is finished to a thickness of approximately 50 μm as shown in FIG. Form.

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

Next, as shown in FIG. 6, holes are formed in the thermal oxidation film 11 on the back surface to form the collector electrode 12, and holes are also formed in the thermal oxide film 7 on the front surface to form the base electrode 13 and the emitter electrode 14. .

Further, the silicon substrate 1 is selectively etched from a position corresponding to the back surface of the oxide layer 6 to form a mesa groove 15.

When forming the mesa groove 15, HF-HNO3CH3CO
When an OH-based etching solution is used, the etching rate for the oxide layer 6 is slower than the etching rate for the silicon substrate 1, so the depth of the mesa groove 15 almost stops when it reaches the bottom of the oxide layer 6. It's convenient.

Finally, a wear-resistant layer 16 such as SiO is formed on the entire back surface that is in contact with the thermal paper.

A region surrounded by oxide layer 6 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 from each other by the thermally insulating oxide layer 6 and air by the mesa groove 15, clear printing is possible with less heat leakage.

Note that although an example using a P/P-substrate has been described above, it is also possible to use other substrates.

Furthermore, if it is necessary to lead out the collector electrode 12 to the front side of the silicon substrate 1, various methods can be applied.

For example, a thin film forming method with excellent throwing power such as an OVD method, a sputtering method, or a plating method may be used to conduct electricity through an insulating film on the side surface of a hole penetrating the front and back sides of the silicon substrate 1 or on the side surface of the end of the silicon substrate. By forming the layer, the collector electrode can be led out to the front side of the silicon substrate.

Furthermore, thermal insulation between heating elements can be achieved by using only the oxide layer 6 formed as deep as the finished thickness of the silicon substrate 1, or by using only the mesa groove 15 as deep as the finished thickness of the silicon substrate 10. Of course it is achievable.

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

As shown in Fig. 6, the collector saturation resistance is the one in which the P-type epitaxial layer 2, the P~-type silicon substrate 1, and the P-type diffusion layer 10 are connected in series. Since it is the P-type silicon substrate 1 that shows this, it is mainly the P-type silicon substrate 1 that generates heat.

In other words, since the heat-generating portion is located relatively close to the thermal paper, the thermal resistance from the heat-generating portion to the thermal paper is smaller than that of Conventional Example C, resulting in a thermal printing head with high heat generation efficiency.

Furthermore, since the transistors in the thermal printing head of the present invention are vertical rather than horizontal as in the past, there is no need to form a collector contact on the front side, so the dot area is larger than in the conventional thermal printing head for the same dot area. It is possible to take a collector current, thus enabling low voltage driving.

Also, even though the dot density becomes higher and the area where a transistor can be formed becomes smaller, the emitter area can be much larger than that of a conventional lateral transistor, so it is possible to handle enough power to color thermal paper. This enables the production of high-density thermal printing heads.

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

Since there is no PN junction on the side that contacts the thermal paper, even if cracks occur in the wear-resistant layer 16 due to changes over time, problems such as deterioration of the withstand voltage of the PN junction and increase in leakage current as in the conventional example will not occur. This results in a highly reliable thermal printing head.

As described above, the thermal printing head of the present invention has various advantages and is of great industrial value.

[Brief explanation of drawings]

1 to 6 are cross-sectional views showing an embodiment of the thermal printing head of the present invention in the order of steps. 1... Semiconductor substrate, 6... Oxide layer,
8...Base, 9...Emitter, 10
...Diffusion layer, 12...Collector electrode,
15... Mesa groove, 16... Wear resistant layer.

Claims (1)

[Claims] 1 An emitter and a base are provided on the first main surface of the semiconductor substrate that does not contact the thermal paper, a collector contact is provided on the second main surface that contacts the thermal paper, and the resistivity of the collector region is such that the specific resistance of the collector region is in the thickness direction of the semiconductor substrate. It is characterized by configuring a transistor with a structure in which the specific resistance is not uniform but relatively higher on the second main surface side than on the first main surface side, and the collector saturation resistance of this transistor is made to generate heat. Thermal printing head.