JPH0245165A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain a thermal-head, in which a driving element being difficult to be broken, having excellent reliability, enabling high integration and high- speed operation and having low voltage and high current characteristics and a heating element are unified, by composing the driving element joined with the heating element of a bipolar-transistor having a hetero-junction and forming the heating element of a polycrystalline silicon layer, grain size of which is increased through laser irradiation. CONSTITUTION:A bipolar-transistor having an n-p-n type hetero-junction and a heating element region 10 are shaped onto an insulating base body 1 such as a quartz substrate, a sapphire substrate, etc. A p-n-p type may also be used as the transistor having the hetero-junction as a driving element besides an n-p-n type. An n<+> type silicon seed layer 2 on the insulating base body 1 is crystallized through the energy beam irradiation with electron beams, etc. High currents can be acquired easily at low voltage under the state of the grounding of a base electrode 6 in the characteristics of the transistor, thus manufacturing the element enabling high-speed operation. Accordingly, the degree of integration is improved, and high accurate printing is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] This invention relates to thermal heads used in coprinters, copying machines, etc.

[Conventional miscellaneous Vq] As conventional technology, Mi, crocomputer
Conference in Japan '8
8 PrΦceeding P.

96-94 "Integrated thermal head using rOMO8 ultra-thin film transistor" This is a method to create a field effect transistor using a polycrystalline silicon thin film 14 as a semiconductor layer on a quartz substrate 15, as shown in FIG. Then, the heating element 18 is made of the same material as the gate electrode 15,
This was to realize a thermal head that was integrated into a heating element for one day using a field effect transistor as a driving element.

[Problem to be Solved by the Invention] However, in such a conventional thermal head, a polycrystalline silicon thin film 14, which becomes a semiconductor layer of a field effect transistor, is directly formed on a quartz substrate 15, which is a type of insulating substrate. In order to achieve high characteristics, it was necessary to form the polycrystalline silicon film 14 very thinly, approximately 400 mm thick.As a result, conventional polycrystalline silicon The effective mobility is about 10 times thicker than that of a field effect transistor using a semiconductor layer (However, on the other hand, since the polycrystalline silicon thin film 14 is very thin at about 400 Ω, the source electrode 16 in contact with the polycrystalline silicon thin film 14 Poor contact with the drain electrode 17 is likely to occur, and even if the effective mobility is 45 to 80 eta/V-sec, it is about 10 times the effective mobility of a conventional field effect transistor whose semiconductor layer is polycrystalline silicon. Even if improved, the effective mobility was only about one-tenth of the value of a field-effect transistor with a single-crystal silicon semiconductor layer.For this reason, a device with a channel width of 20 μm and a channel length of 7 μm could obtain When the source electrode 16 is grounded, the current characteristics are as follows:
The current flowing between the drain electrode 17 and the source electrode 16 by applying 5 volts to ils and 2 volts to the drain electrode 17 is a low current of 1 milliampere or less. Therefore, when driving a thermal head, it is necessary to increase the channel width of the transistor to obtain a high current.
This increased the capacity of the transistors, making high-speed operation impossible, and at the same time making high integration impossible, making it difficult to realize a thermal head that would enable higher-definition printing.

In addition, the polycrystalline silicon thin film 14 constituting the semiconductor layer of the transistor contains many crystal defects, so it tends to change over time and lacks reliability. There was a wholesaler who said that the film 21 was extremely thin at 500 angstroms and was easily damaged by static electricity.

Therefore, in order to solve these conventional problems, the present invention integrates a driving element and a heating element, which are hard to break, have excellent reliability, are highly integrated, and have low voltage, high current characteristics that enable high-speed operation. The purpose is to provide a thermal head with

[Means for Solving the Problems] In order to solve the above-mentioned problems, the thermal head of the present invention has a heating element and a driving element formed on an insulating base, in which a heating element and a driving element are bonded to the heating element. The driving element is a bipolar transistor having a heterojunction, and the heating element is a polycrystalline silicon layer whose grain size has been increased by laser irradiation.

[Examples] Examples of the present invention will be described below based on the drawings. In FIG. 1, a bipolar transistor having an npn type heterojunction and a heating element region 10 are formed on an insulating substrate 1 such as a quartz substrate, a sapphire substrate, a fluoride laminated substrate, a magnesia spinel laminated substrate, etc. Figure 3 shows a perspective cross-sectional view of an example. Note that the bipolar transistor having a heterojunction serving as a driving element may be an npn type as in this embodiment, but may also be a pn:[) type. A sheet layer 2 of n+ type silicon on an insulating substrate 1 is crystallized by irradiation with an energy beam such as an h-laser beam or an electron beam. This n-type silicon seed layer 2
In addition to serving as a seed layer (seed crystal layer) during selective epitaxial growth of the n-type germanium layer 3 that will become the collector region, it also forms the heating element region 10 of the thermal head, and also serves as the n+-type germanium layer that will become the collector region. It also serves as a collector electrode in contact with layer 3. In addition, the presence of this crystallized n-type silicon seed layer 2 facilitates the growth of high-quality crystals on an inexpensive and large-area insulating substrate, making it possible to easily grow a high-quality crystal on an inexpensive and large-area insulating substrate. The crystals of the p+ type germanium layer 4 constituting the base region and the type germanium layer 5 are of good quality. Therefore, the characteristics of the bipolar transistor having a heterojunction created in this way are as shown in FIG. 4, as shown in FIG. Becomes an element. The size of the device of this example exhibiting this characteristic is 5
The size of the element is 0 μy×50 μm, which is small. Therefore, high integration is possible, and a thermal head capable of high-definition printing can be realized.

As explained above, since the crystal layer formed on the n-type silicon seed layer 2 in FIG. It is more stable and has a longer lifespan than the manufactured element. Next, FIG. 2 shows a perspective sectional view of an embodiment in which the types of materials of the films constituting the collector region and space region of a bipolar transistor having a heterojunction are changed. The difference from the bipolar transistor having a heterojunction shown in FIG. 1 is that the collector region of the transistor shown in FIG. 2 is an n-type silicon layer, and the space region is a p+-type silicon layer. The emitter region is an n+ type silicon layer 5 in both the embodiments shown in FIG. 1 and FIG. Both embodiments are bipolar transistors having an npn-type heterojunction in which the six regions of the flexor, base, and emitter are composed of n-type, p-type, and n-type semiconductor layers, and the basic operation is the same. There is a wide range of materials to choose from. In addition, it is also possible to use GaAs or AtGaAs. FIG. 3 is a perspective cross-sectional view showing an example in which the same bipolar transistor having a heterojunction shown in FIG. 2 is manufactured by a different process. The difference from the device in FIG. 2 is that in FIG. 3, the emitter electrode 7 and the n
9 silicon layer 5 are formed at the same time, simplifying the process, and interlayer insulating film 8 is sandwiched between the emitter electrode Z and the space electrode 6 intersects three-dimensionally. A bipolar transistor having a heterojunction having such a structure has no operational problems, and the manufacturing process can be easily simplified.

[Effects of the Invention] As explained above, the thermal head of the present invention can be used on various types of inexpensive, large-area insulating substrates by fabricating a bipolar transistor having a heterojunction and a heating element on an insulating substrate. This has the effect of realizing a thermal head that has a long life, high integration, low voltage, high-speed operation, and can easily perform high-definition printing.

[Brief explanation of the drawing]

FIG. 1 is a perspective sectional view showing an embodiment of the thermal head of the present invention. 2 and 3 are perspective sectional views showing other embodiments of the thermal head of the present invention. FIG. 4 is a diagram showing the current/voltage characteristics of a bipolar transistor having a heterojunction in the embodiment of the thermal head of the present invention. FIG. 5 is a perspective sectional view of a conventional thermal head. 1...Insulating base 2...N+ type silicon seed layer 6...
・・・・・・N-type germanium layer 4・・・・・・・・・
・p+ type germanium layer 5......n+79
37 Layer 6...Pace electrode 7...Emitter electrode 8...Interlayer insulating film 9...Insulating film 10 ... Heating element region 11 ... N type silicon layer 12 ... P + type silicon layer 13 ... Quartz substrate 14 ... Polycrystalline silicon Counterfeit 5...Gate electrode 6...Source'wL pole 7...Drain electrode 8...Heating element 9...Source wiring 0 ...Gate wiring 1...Gate insulating film or higher

Claims (1)

[Claims] In a thermal head in which a heating element and a driving element are built on an insulating substrate, the driving element connected to the heating element is made of a bipolar transistor having a heterojunction, and the heating element is made to have a large particle size by laser irradiation. A thermal head characterized by being made of a polycrystalline silicon layer.