JPS5973973A - Heat sensitive recording head - Google Patents

Abstract

PURPOSE:To reduce the heat capacity of a heat generating part to a large extent to enable high speed recording, by a method wherein a bridge part is formed to a silicon wafer by anisotropic etching and heat generating resistance is formed on said bridge part. CONSTITUTION:A silicon wafer 6 is covered with an etching mask 9 and anisotropic etching is applied to the hole provided to said mask 9 to form a bridge part l' of the silicon wafer 6 while leaving an etch stop layer 7. An electric insulating layer 8, heat generating resistance 3, a lead wire 4 and a surface protective layer 5 are provided on the bridge part l' of the silicon wafer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording head, and particularly to a thermal recording head used in a thermal printing device.

The thermal recording method is a low-noise, primary color recording method, and the device mechanism is simple and maintenance-free, and the device and recording paper are relatively low-cost, so it has become the main recording and printing method used in printers, facsimile machines, etc. It has become. Printing using this thermal recording method uses a thermal recording head consisting of multiple fine heating resistors, and selectively energizes the heating resistors according to pixel information to generate heat to record colors on thermal recording paper. Since this method utilizes a phenomenon, it has the drawbacks that the recording energy per pixel formation is low and the recording speed is slow compared to other recording methods. In recent years, efforts have been made to improve the characteristics of red thermal recording paper and the thermal recording head in thermal recording systems, and to improve power efficiency and printing speed, but this is still not sufficient.

First, a conventional thin film type thermal recording head has a structure of a heat generating part as shown in FIG. It has a structure in which an electrode 4 is formed and covered with a surface protective film 5.

Generally, Ta2051 or the like is inserted between the glass glaze 2 and the heating resistor 3 as a reaction prevention or etch stop layer, and a surface image retention layer is 5I for oxidation prevention.
02, a structure with a large number of layers is used, such as a two-layer structure made of Ta205 or the like, as the wear-resistant layer.

In such a thermal recording head, an aluminum substrate is used because power efficiency and one-time printing depend on the thermal characteristics of the substrate. However, since an alumina substrate has good thermal conductivity, when a heating resistor is formed directly on an alumina substrate, a large amount of heat is dissipated to the substrate, making it difficult to crystallize the temperature on the surface of the heating element. Therefore, by providing glazed glass with low thermal conductivity on an alumina substrate, power efficiency is improved by utilizing the heat storage effect of G specific heat generated by the heating resistor. However, the use of a glass glaze heat storage layer also increases the time constant for cooling the heat generating resistor element, resulting in printing quality problems such as trailing and smearing in high-speed printing. It is necessary to take both of these into consideration and determine the optimal glaze thickness according to the conditions for 1ψ. Usually, a thickness of about 30 to 100 microns is adopted, and the power efficiency is about 0.8 to 1.0 microns in a thermal recording head with a power efficiency of 8 dots/mm in the main scanning direction and 7.7 lines/mm in the sub scanning direction. The printing energy required is 0 millijoules/dot, and the maximum printing speed is about 5 milliseconds/line, which has now been achieved and is approaching its limit, thanks in part to the development of constituent materials such as heating resistors. There is.

As described above, it is judged that the main factor inhibiting power efficiency and printing speed is that the specific heat near the heating resistor, especially the glaze glass layer, is large and the effective heat capacity is large.

Based on the above knowledge, the present invention forms a heat generating part in a cross-linked manner in order to greatly reduce the effective heat capacity of the heat generating part, thereby achieving high printing efficiency and high speed printing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal recording head that improves conventional thermal recording heads and provides high power efficiency and high printing speed.

Still another object of the present invention is to provide a heat-sensitive recording head in which a heat-generating portion is formed in a cross-linked manner in order to greatly reduce the effective heat capacity of the heat-generating portion.

According to the present invention, in a thermal recording head having a silicon wafer substrate and a heat generating resistor, a bridge portion formed by anisotropic etching of the substrate, and a heat generating resistor provided on the bridge portion. A thermosensitive recording head having the following characteristics can be obtained.

Further, according to the present invention, there is provided a thermal recording head according to item 1 of the claimed scope of the patent, characterized in that the heating resistor and the corresponding bridge portion formed on the silicon wafer substrate are arranged in a staggered pattern. Gai! I get caught.

An actual example of the present invention will be described below with reference to the drawings.

FIGS. 2A and 2B show a plan view of a thermal recording head according to an embodiment of the present invention and its a-a' cross section. In FIGS. 2(a) and 2(b), in this embodiment, a heating resistor 3, a lead electrode 4, and a surface protection layer 5 are formed on a substrate consisting of a silicon wafer substrate 6, an etch stop layer 7, and an electrical insulating layer 8. be done. The silicon wafer substrate 6 is anisotropically etched through the hole (length 1) of the etching mask 9 to form a trapezoidal groove shown at 2N-). In the etch stop layer 7, [Jl' of the groove at the interface is formed in a bridged manner, and a heating resistor is formed in this bridged portion, and this heating resistor 3 is connected to the surface protection layer 1-5 and the electrical insulating layer 8.
and an etch stop layer 7.

Although the etch stop layer 7 may be formed of a material that is not affected by the anisotropic etching solution for silicon wafers, it is preferable to use a boron-doped silicon layer from the viewpoint of residual strain. Further, the electrical insulating layer 8 can be made of a silicon thermal oxide film, or of course may be formed by forming a film of 5iO1, 8i1N4, or the like.

The heat-sensitive recording head of this embodiment can reduce the thickness of the heat generating part, and does not have a glass layer with a large specific heat, and the thickness of the electrically insulating layer, such as 5in2, is less than 1 micron. Since only a small amount of heat is required, the overall heat capacity of the heat generating part can be greatly reduced.

Therefore, the amount of heat generated by the heating resistor 3 generates a high temperature because the heat capacity of the heating part is small and heat dissipation to the substrate part is almost prevented, which effectively colors the thermal paper. . Furthermore, since the amount of heat accumulated in the heat generating part is small after the energization ends, trailing or blurring of the print does not occur, and high-speed printing is realized along with improved power efficiency.

The outline of the manufacturing process of the thermal recording head of this example is explained in the third section.
As shown in the figure. In FIG. 3, the double-sided polished substrate 6 is (
(100 mm) with a thickness of 0.20 mm as shown in b).
) is a silicon wafer substrate, and this substrate 6 has a silicon layer 7 doped with PPM boron as shown in (b).
A 5 micron film is formed by the CVD method. After this, the board 6
(As shown in /→, a 0.3 micron 8i01 film 8 is formed on both sides by thermal oxidation.This substrate is coated with an 8i02 layer 9 on the back side as shown in ()). A mask hole 9' for anisotropic etching of the J-con is formed by photolithography. By using ethylene diamine, pyrocatechol, and water, which are anisotropic etching solutions for silicon substrates, the (111) plane of the silicon layer 6 is not etched, and the interface between the four (111) planes and the etch stop layer is etched. A depression 6' serving as a top surface is formed. The relationship between the diameter l of the mask hole 9' and the diameter l' of the top surface is l=1.4d+l' with respect to the thickness of the silicon substrate d, and in this example, l is 0.
．． Assuming 39 mm, 1/ obtained 0.11 mm.

On the substrate 6 obtained in the above steps, a heat generating resistor 3 and lead electrodes 4 were formed as shown in FIG.

Here, the heating resistor 3 is made of a Ta-8iC sputtered film.
The electrode 4 is made of AI, and the heating resistor and electrode are patterned so as to be flush with the bridge portion of the substrate. Furthermore, a surface storage layer lO
The surface was covered with a 3 micron thick sputtered film of SiC. Finally, it was mounted on an aluminum plate.

It should be noted that the thermal recording head of this example does not necessarily need to follow the manufacturing process described in this example; for example, the silicon substrate may be anisotropically etched after the entire heated portion is formed, or an anisotropic etching liquid may be used. KOH or the like may also be used. Furthermore, a silicon oxide film or a silicon nitride film may be used as an etch stop layer or mask material. In this case, it can also be used as an electrical insulating layer.

The thermal recording head of this example has 32 x 32 pixels (dots).
This is a serial printer head for printing kanji characters, and as shown in Figure 4 (a) and (b), a total of 32 meandering heating resistors are arranged in a houndstooth pattern at a pitch of 106 microns. There is. Arranging in a houndstooth pattern has the advantage of avoiding thermal effects between adjacent pixels (dots) and forming a large heating element, but in this example, the heating part is placed on the bridge. This also has the effect of compensating for the lack of mechanical strength of the foot.

A thermal recording head having a heat generating part with the same pattern as that of this example was fabricated on an ordinary glazed alumina substrate, and the characteristics were compared. The head of this example achieved high-speed printing of 60 characters/second, which corresponds to 0.5 milliseconds/line, with good printing quality at a printing energy of 0.2 millijoules/dot. This is about one-third the printing energy and about six times the printing speed compared to when a glazed alumina substrate is used.

As explained above, the present invention aims to reduce the heat capacity of the heat generating part by etching the silicon substrate to provide a depression near the heat generating resistor, thereby creating a thermal recording head suitable for high power efficiency and high speed printing. is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the cross-sectional structure of the entire heating part of a general thin film type thermal recording head, FIG. 2 is a diagram showing the structure of a thermal recording head that is an embodiment of the present invention, and FIG. 3 is a diagram showing the structure of a thermal recording head that is an embodiment of the present invention. FIG. 4 is a diagram schematically showing the structure of a serial printer head using an example of the present invention. DESCRIPTION OF SYMBOLS 1...Alumina substrate, 2...Glass glaze, 3...Heating resistor, 4...Mark/lead electrode, 5...Surface film retaining layer , 6...Silicon substrate, 6'...Top depth, 7...Etch stop layer, 8...Electric insulation layer, 9...Etching mask , 9′...Mask hole. Figure / Figure Z Figure 3 Figure 4

Claims (2)

[Claims] (1) A thermal recording head having a silicon wafer substrate and a heat generating resistor, including a bridge formed by anisotropic etching of the substrate and a heat generating resistor provided on the bridge. A thermal recording head featuring (2) The heat-sensitive recording head according to claim 1, wherein the heating resistors and the corresponding bridge portions formed on the silicon wafer substrate are arranged in a staggered pattern.