JPH0737146B2 - Thin film thermal head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermal head for performing heat-sensitive recording on heat-sensitive recording paper by selective heat generation of heat-generating resistors, and particularly to heat-generating resistors and their driving. The present invention relates to a thin film thermal head having a circuit portion formed by thin film technology.

[Outline of Invention]

According to the present invention, a thin film layer made of polycrystalline silicon is provided on an insulating substrate to form a heating resistor and a driving circuit section on the same substrate by using the polycrystalline silicon thin film, and the driving circuit section is formed as an active layer. It is an object of the present invention to provide a thermal head that is composed of thin thin film transistors, can be downsized, has less size restrictions, and can perform high-speed recording and high-gradation recording.

[Conventional technology]

Conventionally, in a line-type or serial-type thermal head, either a direct drive method or a diode matrix method has been mainly adopted as a method for driving a heating resistor. In such a type of thermal head, semiconductor device pellets such as ICs and diodes that constitute the drive circuit section and the like are directly mounted on the thermal head substrate to reduce the size.

However, in the method of mounting the semiconductor element pellets on the substrate as described above, there are many restrictions in terms of downsizing of the thermal head and productivity, and improvement thereof is desired.

For example, as shown in FIG. 6, the thermal head substrate (10
1) When the semiconductor element (102) is mounted on and is sealed with the sealant (103), the protrusions or the protrusions of the cover (104) due to the semiconductor element (102) and the sealant (103). It is necessary to allow the platen (105) to escape from the paper path corresponding to the outer diameter, and the distance W ₁ from the heating resistor to the protrusion of the semiconductor element (102) is restricted, which hinders miniaturization. ing.

On the other hand, the substrate dimension W ₂ is determined by the length of the semiconductor element (102) and the wire bonding pitch. In this case, the semiconductor element (102) can be made small to some extent if it is made into an LSI, but it becomes expensive. In addition, the wire bonding pitch is also a limit of about 150 to 200 μm. For example, if the semiconductor element (102) is a 32-bit driver, about 3 mm is required, and if it is a 64-bit driver, about 7 mm is required. .

In addition, 1) there are many connection points such as wire bonding, soldering, and thermocompression bonding, and the reliability is low. 2) Semiconductor element mounting process is required, and expensive equipment such as wire bonder and resin curing oven is required. As well as
Since it is a work that requires skill, the number of workers is limited. 3) For example, there are many auxiliary materials such as IC pellets, silicone encapsulation, encapsulation cover, Au wire, die bonding paste, etc. 4) For example, when an attempt is made to provide a counter circuit, a temperature sensor circuit, a memory circuit, etc. on the thermal head substrate (101), an IC pellet different from the semiconductor element (102) will be added. There are many problems, such as the fact that it becomes necessary and expensive, including implementation costs.

Therefore, a so-called thin film thermal head has been proposed in which a drive amplifier and a recording control circuit for driving a recording element composed of a heating resistor are composed of thin film transistors, as described in JP-A-58-153672, for example. There is.

However, in a thermal head having a drive circuit section composed of such a normal thin film transistor, the electron mobility μ in the thin film transistor is low, and therefore when it is used for a large current switch, the peripheral length of the gate is required to be very large. In addition to causing size increase and restriction on size reduction, large driver ON resistance, large power loss and poor efficiency,
The frequency characteristics of the field-effect transistor are poor, and it is difficult to cope with high frequencies of about 4 to 6 MHz, and high-speed recording and high-gradation recording are difficult.

[Problems to be solved by the invention]

As described above, the conventional thermal head has many restrictions on miniaturization, which is disadvantageous in terms of productivity and manufacturing cost. Further, a thermal head using an ordinary thin film transistor in a drive circuit section has been proposed, but it is difficult to cope with high speed recording, high gradation recording, etc. due to its characteristics.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and provides a thin film thermal head which has less restrictions on the substrate size, can be downsized, and is advantageous in terms of mass productivity, manufacturing cost, and the like. It is also an object of the present invention to provide a thin film thermal head capable of coping with high speed recording and high gradation recording.

[Means for solving problems]

In order to achieve the above-mentioned object, the thin film thermal head of the present invention provides a thin film layer made of polycrystalline silicon on an insulating substrate and uses the polycrystalline silicon thin film to form a heating resistor and a drive circuit unit on the same substrate. And the drive circuit section has an active layer made of polycrystalline silicon.
It is characterized in that it is composed of a thin film transistor having a thickness of 0 Å or less.

[Action]

Since the drive circuit portion is formed by the polycrystalline silicon thin film layer on the insulating substrate, the protrusion by this drive circuit portion is several μm.
It can be suppressed to the following, and the restriction on the substrate size is solved. At the same time, complicated processes such as wire bonding are not required and reliability is increased.

Also, especially in the drive circuit part, the electron mobility μ is set by setting the thickness of the polycrystalline silicon thin film layer, which is the active layer of the transistor forming the drive circuit, to 800 Å or less and setting it to a thickness almost equal to the depletion layer. Is increased, and a driver element of several mA to several tens of mA is manufactured in a minute area. Further, the operating frequency of the logic circuit becomes relatively high, and high speed recording and high gradation recording can be achieved.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

First, FIG. 5 shows a circuit configuration example of a thin film thermal head to which the present invention is applied.

In this circuit configuration example, the image signal is input as a data signal from the signal terminal (51) to the shift register circuit (52). When one line of data is input to the shift register circuit (52) according to the clock signal input from the signal terminal (53), all data is latched by the strobe signal input as a latch pulse from the signal terminal (54). It is transferred in parallel to (55) and held. The data held in the latch circuit (55) is input from the signal terminal (56) and drives the driver element (58) through the gate circuit (57) in accordance with the instruction of the enable signal that determines the printing timing and the like, and the heating resistor is generated. The body (59) is selectively energized to generate heat.

In the present invention, for example, the driver element (58) is replaced by a MOS FET.
Then, other circuits are configured with CMOS, and the film thickness of polycrystalline silicon of these source and drain active layers is set to 800 Å or less.

FIG. 1 shows an example of a thin film thermal head to which the present invention is applied. The active layer of the MOS FET constituting the driver part is used as a heating resistor, and the source and drain electrodes are used as electrodes of the heating resistor. It is a thing.

In this example, on the substrate (1) of the thermal head, SiO ₂
An insulating film (2) such as is formed on the entire surface, and a polycrystalline silicon thin film (3) is formed on the insulating film (2). As the material of the substrate (1), quartz, glass, glaze ceramic, etc. can be used, and a convex substrate (for example, a partial glaze substrate etc.) in which a portion where a heating resistor is formed is slightly raised. Is also good. Further, the insulating film (2) is not always necessary, and may be omitted in some cases.

The polycrystalline silicon thin film (3) is used as an active layer that constitutes a heating resistor and a thin film transistor of a drive circuit section.

That is, a predetermined n is provided at both ends of the polycrystalline silicon thin film (3A) of the drive circuit portion of the polycrystalline silicon thin film (3).
Low-resistance n-type region (3a) doped with type impurities,
(3b) is formed, and these n-type regions (3a) and (3b) having a low resistance respectively form a source region (4) and a drain region (5). During operation of the MOS FET, a channel is formed in the polycrystalline silicon thin film (3A) between the source region (4) and the drain region (5). The intermediate portion of the crystalline silicon thin film constitutes the active layer (3c).

A gate insulating layer (6) made of SiO ₂ is formed on the polycrystalline silicon thin film (3A), and impurity-doped polycrystalline silicon (DO) is formed on the gate insulating film (6).
A gate electrode (7) made of POS) is formed. As the material of the gate electrode (7) is not limited to polycrystalline _{silicon, Ta-SiO 2, Ta-} Si, TaN, NiCr or the like is used.

Further, an insulating layer (8) made of SiO ₂ is formed on the polycrystalline silicon thin film (3A) and the gate electrode (7). Openings (8a) and (8b) are formed in the insulating layer (8), and Al and W for the source region (4) and the drain region (5) are formed through these openings (8a) and (8b). , Ti,
Extraction electrodes (9) and (10) made of Mo or the like are formed, respectively.

By the way, in the FET having the above-described structure, the film thickness of the polycrystalline silicon thin film (3A) forming the active layer (3c) in which the channel is formed is about 1500 Å, which is the usual thickness in the present invention. The thickness is set to 800 Å or less, which is extremely thin.
Therefore, the effective electron mobility μ can be made extremely large. This is because the film thickness of the active layer (3c) is smaller than the channel thickness induced in the active layer (3c) when a gate voltage of a normal magnitude is applied to the gate electrode (7). It is thought to be because of this. The thickness of the polycrystalline silicon thin film (3A) is 20 to 800.
It may be set in the range of Å, but practically, it is preferable to set it to about 200 Å.

On the other hand, the polycrystalline silicon thin film, which is a constituent material of the active layer (3c), is used not only in the drive circuit section but also in the heating resistor (3c).
Also used as B).

Further, a lead electrode (11) formed at the same time when the extraction electrodes (9) and (10) are formed is connected to the polycrystalline silicon thin film which becomes the heating resistor (3B). In this example, the extraction electrode (9) of the source region (4) and one lead electrode (11a) are integrally formed to electrically connect the drive circuit section and the heating resistor. Wiring between the active elements of the drive circuit section is performed by, for example, wiring for enable, latch, data, clock, etc. using a gate electrode material having a relatively high wiring resistance, and V _H , G _H , V _D , G _D, etc. It is also possible to use a two-layer wiring such that the wiring is performed with the electrode material of the source electrode and the drain electrode.

An oxidation resistant layer (12) and a wear resistant layer (13) are formed on the entire surface of the heating resistor and the drive circuit section having the above-mentioned configuration. The oxidation resistant layer (12) and the abrasion resistant layer (13) serve as a protective film for the heating resistor (3B) and at the same time act as a surface protective film (passivation film) for the FET in the drive circuit section.

In the thin film thermal head configured in this way,
Since the driver of the drive circuit unit is composed of the thin film transistor circuit, the dimension t of the protrusion in FIG. 6 can be suppressed to almost zero (several μm or less), and therefore, the dimension restriction on the paper path can be eliminated. Also,
The drive circuit unit can be installed anywhere, which is also advantageous for downsizing.

Further, since the drive circuit unit and the heating resistor are connected by a thin film pattern, wire bonding is not required, and the dimensional constraint due to the pitch constraint can be eliminated,
At the same time, complicated processes, expensive equipment, and auxiliary materials attached to bonding become unnecessary. In particular, without using the IC chip,
Since there are no connection points, the reliability is high.

Furthermore, since the heating resistor and the active element of the drive circuit section are formed in the same step on the same substrate, the manufacturing cost is almost the same regardless of which circuit is formed, and the practicality is high.

Although the embodiment in which the active layer of the MOS FET forming the driver section is used as the heating resistor has been described above, the present invention is not limited to this embodiment, and it goes without saying that various configurations can be adopted. Yes. Another embodiment of the present invention will be described below.

FIG. 2 shows an example in which the gate electrode of the FET is used as a heating resistor. The same applies to each of the following examples, but the same members as those in the previous embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the heating resistor (21) is formed of the gate material at the same time when the gate electrode (7) is formed. Further, the lead wire of the heating resistor (21) is formed of these electrode materials at the same time when the extraction electrodes (9) and (10) of the source region (4) and the drain region (5) are formed. It is similar to the previous embodiment.

FIG. 3 shows that the polycrystalline silicon thin film (3) for forming the active layer (3c) of the FET is used as the heating resistor (3B) as well as the insulating layer (as in the embodiment shown in FIG. 8)
Is used as the oxidation resistant layer of the heating resistor (3B). In this case, the oxidation-resistant layer is
Since the structure is formed on B), unlike the embodiment shown in FIG. 1 or FIG. 2, a special oxidation resistant layer (12) is not required and only the wear resistant layer (13) is formed. Good.

FIG. 4 shows that the gate material for forming the gate electrode (7) of the FET is used as the heating resistor (21) as in the embodiment shown in FIG. The example shown is used as an oxidation resistant layer of a heating resistor (21). Also in this example, as in the embodiment shown in FIG. 3, the oxidation resistant layer (12) is unnecessary.

In addition, the heating resistor is Ta-
It is also possible to use a material such as SiO ₂ , Ta-Si, TaN, or NiCr, and connect the heating resistor and the thin film transistor with the electrode material of the thin film transistor.

〔The invention's effect〕

As is clear from the above description, in the thin film thermal head of the present invention, the heating resistor and the drive circuit section are formed on the same substrate by the thin film technique, and the heating resistor and the drive circuit section are gated. Since the wires are connected by a thin film pattern of material, electrode material, etc., connection by wire bonding becomes unnecessary, and the productivity and reliability are excellent.

Further, the drive circuit unit is composed of thin film transistors,
The amount of protrusion of this part from the substrate is extremely small (total of several μ
Since it is about m or less), there is no restriction on the mounting position due to the outer diameter of the platen and the like, which is extremely advantageous in terms of downsizing.

Furthermore, since the thickness of the active layer of the thin film transistor that constitutes the drive circuit portion is set as thin as 800 Å or less, the electron mobility μ becomes extremely high, and the transistor that is the driver element can be formed in a small area. This point is also advantageous for downsizing.

Furthermore, the thinning of the active layer is highly practical not only for downsizing the thermal head but also for improving recording characteristics. For example, since the on resistance of the driver element can be reduced, power loss is reduced and efficiency is greatly improved. Further, the frequency characteristics of the FET can be improved, and thus high speed recording and high gradation recording can be performed.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part showing an embodiment of a thin film thermal head to which the present invention is applied. 2 to 4 are enlarged cross-sectional views of essential parts showing other embodiments of the present invention. FIG. 5 is a circuit diagram showing a circuit configuration example of the thermal head. FIG. 6 is a side view schematically showing a conventional thermal head. 1 ... Substrate 3 ... Polycrystalline silicon thin film 3c ... Active layer 3B, 21 ... Heating resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display part 113 K

Claims (1)

[Claims] 1. A thin film layer made of polycrystalline silicon is provided on an insulating substrate, and a heating resistor and a driving circuit portion are formed on the same substrate by using the polycrystalline silicon thin film. A thin-film thermal head characterized by comprising a thin film transistor having an active layer made of crystalline silicon and having an active layer of 800 Å or less.