JPH03234552A - Thermal printing head - Google Patents

Abstract

PURPOSE:To make the temperature of a heating element approximately constant, uniformize a printing temperature, and perform a sharp printing by providing a temperature sensor for regulating a printing current in accordance with the temperature of the heating element heated by a printing current supplied from a printing drive circuit part. CONSTITUTION:A temperature sensor 5 is provided which regulates a printing current to be supplied from a printing drive circuit part 3 to a heating element 4 in accordance with the temperature of the heating element 4 heated by a printing current supplied from the printing drive circuit part 3. With the increase of the temperature of the heating element 4, in accordance with the heat the temperature sensor 5 decreases a printing current supplied from the printing drive circuit 3 to the heating element 4. On the contrary, with the low temperature of the heating element 4, the temperature sensor 5 increases a printing current supplied from the printing drive circuit 3 to the heating element 4. In this manner, without conducting a complicated printing history control, the temperature of the heating element at the time of printing can be made approximately constant. Therefore, a uniform printing density and a sharp printing can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal print head that performs thermal recording.

The thermal print head used for this purpose has a structure in which a print drive circuit is connected to a large number of heating elements arranged on a substrate. The print drive circuit section includes a shift register circuit, latch circuit,
The print data is sequentially input to the shift register circuit according to the clock signal, and the input print data is transferred in parallel to the latch circuit by the latch signal and held, and the held print data is used to adjust the print timing, etc. The strobe signal that determines opens the gate of the latch circuit and is input to the drive element.

In such a thermal print head, when print data is input to the drive element of the print drive circuit, the drive element selectively sends current to the heating element to generate heat, and this heat is directly applied to the thermal paper. Heat-sensitive recording is performed, or heat-sensitive recording is performed on recording paper via a heat-sensitive ink sheet.

[Prior Art] Conventional 1 Heat-sensitive recording by selective heat generation of heat generating elements [Problems to be Solved by the Invention] However, in the above-mentioned thermal print head, the spacing between the heat generating elements is small, or the heat generating operation is fast. If this is repeated, the next heating will be performed before the heat of the heating element has cooled down sufficiently, causing the temperature of the heating element to rise more than necessary, resulting in uneven printing density and the inability to print clearly. The problem is that it disappears.

To prevent this, in the past, the temperature rise of each heating element was predicted based on the number of times of printing on each heating element, and based on this prediction, the pulse width of the strobe signal, etc. was adjusted to control the driving of the heating element by the drive element. By doing so, printing history control is performed that adjusts the amount of heat generated by the heating element to prevent the temperature of the heating element from rising more than necessary. but,
This printing history control is performed not by detecting the actual temperature of the heating element, but by predicting the temperature rise, so it is extremely difficult to determine control conditions, and moreover, it is difficult to determine the control conditions, and it is necessary to use external printing data, strobe signals, etc. Since control data must be included in the print drive circuit, there is a problem in that the print drive circuit becomes extremely complex. In particular, in a high-density thermal print head with a large number of heating elements, a large amount of data must be sent in a short period of time in order to drive at high speed, and five circuits are required to operate at high speed. In this way, there are various problems in controlling the heat of the heating element by controlling the print history.

An object of the present invention is to provide a thermal print head that can maintain the temperature of a heating element during printing to almost the same temperature without performing complicated print history control, and that can print clearly with uniform print density. It is.

[Means for Solving the Problems J] In order to achieve the above-mentioned object, the present invention has the following features: The printer is equipped with a temperature sensor that adjusts the printing current supplied to the printer.

[Function] According to the present invention, when the heating element repeatedly generates heat due to the printing current from the printing drive circuit section and the temperature of one heating element rises, the temperature sensor is supplied with the heat from the printing drive circuit to the heating element. This reduces the printing current and, conversely, increases the printing current supplied to the heating element from the print drive circuit when the temperature of the heating element is low, so the heating element's power during printing can be reduced without complicated printing history control. The temperature can be kept almost constant, which enables clear printing with uniform print density.

[Embodiment J] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 2 shows the overall configuration of the thermal print head of the present invention. This thermal print head is formed as a rectangular flat plate as a whole, and a heat generating element arrangement section 2 is provided on the right side of the silicon substrate l. , a large number of heating resistor layers (heating elements) 4, which will be described later, are arranged in the 0-shot S element array section 2 in which the print drive circuit section 3 is provided on the left half, and a heating resistor layer (heating element) 4, which will be described later, is arranged on the bottom side of each heating resistor R4. A diode (temperature sensor) 5 is correspondingly provided. The print drive circuit section 3 is composed of a drive transistor (drive element) 6° C-MO 57, connection terminals 8a to 8f, etc. The drive transistor 6 is a thin film MO3ΦFET, and a C-MO
Reference numeral 37 constitutes the shift register circuit 9, latch circuit IO, and the like. The connection terminals 8a and 8b are provided on the connection wiring 11.11 of the shift register circuit 9, the connection terminal 8C18d is provided on the connection wiring 12.12 of the latch circuit IO, and the connection terminal 8e is provided on the connection wiring 12.12 of the drive transistor 6. The connection terminal 8f is provided on the connection wiring 13, and the connection terminal 8f is provided on the common electrode wiring 14 of the heat generating resistance layer 4.

Figure N41 is an enlarged sectional view of the above-mentioned thermal print head. The silicon substrate l is a wafer made of n-type single crystal silicon. On this silicon substrate 1, a heating resistor layer 4 and a diode 5 are formed in N layers on the right side, and a drive transistor 6, a C-MO 37, and a connecting terminal 8 are formed on the left half.
a to 8f are formed all at once. Hereinafter, the configuration of each element will be explained in order.

The diode 5 is of a pn junction type and is formed on the upper right surface of the silicon substrate l. That is, a p-layer region 15 doped with an acceptor impurity such as poron (B) is formed in that portion of the silicon substrate l.
An n-type region 16 doped with a donor impurity such as phosphorus (P) is formed in a part of the layer region 15 . And P
A1. Al-
Electrode wiring 17.1 made of low resistance metal such as 3i, MoJ, etc.
8 is 5i02. They are connected while being wrapped in an insulator 1119 such as SiN. In this case, the insulating film 19 has a two-layer structure,
The structure is such that each electrode wiring 17 and 18 is patterned on the first layer formed, and the second layer is formed on -L thereof. Note that, as shown in FIG. 2, the other ends of the electrode wiring 17 connected to the p-layer region 15 and the electrode wiring 18 connected to the n-type region 16 are connected to drive transistors, which will be described later, through through holes 20, respectively. After overcoming 6, C-MO
It is connected to 37.

The heating resistor layer 4 is a portion that generates heat, and is formed corresponding to the diode 5 described above. That is, on the insulating film 19 on the diode 5, a heat generating portion 21 which is raised in a convex shape is formed over the entire length in the width direction of the silicon substrate. A heat generating resistor layer 4 formed by doping polycrystalline silicon with an impurity is formed over the lower part thereof.The heat generating resistor layer 4 has 16 to 32 dots (16 to 32 dots)/m along the longitudinal direction of the heat generating portion 21.
They are arranged at equal intervals with a pitch of m. Further, the first heating resistance layer 4 has a predetermined sheet resistance (several tens of Ω/hole) by doping a predetermined amount of P ions as an impurity. That is, the total resistance value of the heating resistance layer 4 is determined by the implantation concentration of P ions and its area, and is adjusted by the implantation amount of P ions and the amount of non-etching. It has been adjusted to a certain extent. A common electrode wiring 14 is connected to the right end of the heating resistance layer 4, and an electrode wiring 22 is connected to the left end. Each electrode wiring 14.22 is made of the same material as each electrode wiring 17.18 of the diode 5, and the common electrode wiring 1 on the right side
4 are connected continuously to each heat generating resistor layer 4, and the electrode wirings 22 on the left side are respectively connected to drive transistors 6, which will be described later. These heating resistance layer 4 and each electrode wiring 14.
A protective film 23 is formed on the surface of 22 . This protective film 23 has oxidation resistance and wear resistance, and has 5i
Even if it has a two-layer structure of 02 and 5i11, 5iON
The protective film 2 may have a single layer structure.
3, a portion corresponding to the heat generating portion 21 is formed to protrude higher than the protective film 23 in the entire surrounding area. This structure is extremely effective in bringing the surface of the protective film 23 in the area corresponding to each heating resistor layer 4 into contact with thermal paper, thermal ink sheet, or the like.

The drive transistor 6 is an n-MO5LIFET, and is formed in a portion far leftward from the heating resistance layer 4. That is, a p-type region 24 doped with B ions is formed inside the upper surface of the silicon substrate l in that portion, and two n-type regions doped with P ions are formed within this p-required region 24. A region 25.25 is formed. These two n-type regions 25.25 form source and drain electrodes, respectively. These two n-type regions 25.
The same insulating film 19 as described above is formed on the silicon substrate 1 except for the central part of the p-type bond region 24 including 25.
5iO
A gate electrode a27 surrounded by a gate insulating film 26 consisting of
is formed. This gate electrode 27 is connected to the heating resistance layer 4
Similarly, by doping polycrystalline silicon with P ions, it is formed to have a lower resistance than the heating resistance layer 4.

Further, source and drain electrode wirings 28.28 are connected to the two n-type regions 25.25, respectively. Each of the electrode wirings 28.28 is made of the same material as each of the electrode wirings 17 and 18 described above, and one of the electrode wirings 28.
8 is the heating resistance! It is integrated with the electrode wiring 22 of a4, and the other electrode wiring 28 is connected to the ground connection wiring 13 as shown in FIG. A heating resistor J' is provided on each electrode wiring 28, 28 and gate insulating film 26.
The same protection IFI 123 as in iii'4 is formed. This protection@23 is formed to be lower than the protection HFl 123 of the heating resistance layer 4.

The C-MO 37 is composed of a large number of n-MOS and p-MO 3, and is formed close to the left side of the drive transistor 6 described above. In this case, the n-M O5 has the same structure as the drive transistor 6 described above except that it is formed in a small area for small current, and the P-MOS has two P layers inside the upper surface of the silicon substrate 1. It has the same structure as the drive transistor 6 described above except that regions 29 and 29 are formed. Therefore, the same parts are given the same reference numerals here, and the explanation thereof will be omitted. In addition, P of p-MOS
Of the electrode wirings 28.28 formed on the layer region 29.29, the right electrode wiring 28 is connected to the left electrode wiring &128 of the n-MO5.

The connection terminals 8a to 8f are each connected to a bump electrode ai30 (first
This bump electrode 30 is connected to the insulating film 19 of the silicon substrate 1 through the opening of the protection@23 (only one is shown in the figure).
The protective film 2 is formed on the butt electrode 31 formed in the L shape.
It is provided to protrude above 3. In this case, as shown in FIG. 2, the number of batt electrodes ai31 corresponds to the number of connection terminals 8a to 8f, and each one is connected to a shift register circuit 9. It is connected to the latch circuit 10, the ground connection wiring Mj13 of the drive transistor 6, and the common electrode wiring 14 of the heating resistor layer 4.

Next, with reference to FIGS. 2 and 3, a case will be described in which thermal recording is performed using the above-mentioned thermal print head.

Normally, when print data is supplied to the connection terminal 8a and a clock signal is input to the shift register circuit 9 via the connection terminal 8b, one line of print data is sequentially input to the shift register circuit 9 according to the clock signal. Ru. This print data for 1 line and 2 is transferred in parallel from the shift register circuit 9 to the latch circuit 10 by the latch signal applied to the connection terminal 8c. The print data held in the latch circuit 10 is transferred to the latch circuit 10 by a strobe signal applied to the connection terminal 8d that determines the printing timing, etc.
is inputted to the drive transistor 6 from. That is, the third
As shown in the figure, when the transistor 32 of the latch circuit 1O is opened by the strobe signal, the drive transistor 6
Voo (+5V) is branched between the resistor 33 and the diode 5 and applied to the gate electrode 27 . At this time, since diode 5 is reverse biased, only a small amount of leakage current flows, so VDD remains at almost the same voltage (
+5V) is applied to the gate electrode 27 via the resistor 33 to selectively open the gate of the drive transistor 6. Then, a current selectively flows from the common electrode wiring 14 side to which VH is applied to the ground connection wiring 13 via the heating resistance layer 4 and the drive transistor 6, so that the heating resistance layer 4 generates heat. Thermal printing is performed by the heat generated by the S resistor 4.

In this way, when the heating resistor R4 repeatedly generates heat and performs thermal printing, and the temperature of the 1 heating resistor layer 4 rises to about 200°C, the diode 5 provided under it rises to 100°C. Since it is heated to a certain extent, a leakage current flows through the tie auto 5. This leakage current increases as the temperature rises. For example, when the temperature rises by 10° C., the leakage current increases by about twice. When the leakage current increases, the voltage VDD applied to the drive transistor 6 becomes lower than +5V, so the current flowing through the heat generating resistor R4 decreases.
The current flowing through the heating resistor layer 4 when the temperature is about 1
It decreases to less than half of what it was when it was 0℃ lower. As a result, the amount of heat generated by the heat generating resistance layer 4 is reduced, and a rise in temperature is suppressed. Conversely, when the temperature of the heat generating resistor layer 4 is low, no leakage current is generated in the diode 5, so Woo (+5V) is directly applied to the drive transistor 6, so the current flowing through the heat generating resistor layer 4 increases. , the temperature of the heat generating resistance layer 4 is increased. Note that this temperature control is performed independently for each of the heat generating resistor layers 4 arranged in large numbers.

In this way, according to the above-described thermal print head, when the heat generating resistor layer 4 repeatedly generates heat and its temperature rises by F, the diode 5 intentionally reduces the current flowing through the heat generating resistor layer 4, and the heat generating resistor The temperature rise of the layer 4 is suppressed, and conversely, when the temperature of the heat generating resistor N4 is low, the current flowing through the heat generating resistor layer 4 is increased to raise the temperature of the heat generating resistor layer 4, so the temperature of the heat generating resistor layer 4 during printing is reduced. can be kept almost constant. This enables clear thermal printing with uniform printing density, which was previously required. Not only does an extensive print history circuit become unnecessary, but also there is no need to input data including control information, so the structure of the print drive circuit section 3 becomes simple, and high-speed drive and high-density packaging are possible.

Note that the present invention is not limited to the embodiments described above. For example, temperature control is not limited to the leakage current of the diode 5, but may also be controlled by detecting changes in resistance or capacitance. There is no need to control using a signal, and it may be converted into a digital signal and controlled digitally.

Further, the heating resistance layer 4 does not need to be made of polycrystalline silicon doped with impurities, and may be a high-resistance metal layer or the like.
Also, the substrate does not need to be a silicon substrate, and may be an insulating substrate made of glass, quartz, ceramic, etc. In this case, the temperature sensor may be formed after forming a polycrystalline silicon layer on the insulating substrate. Furthermore, the print drive circuit section 3 does not need to be integrated with the substrate together with the heat generating resistor layer 4 and the temperature sensor, and may be constructed separately.

[Effects of the Invention] As described in detail above, according to the present invention, the temperature sensor is moved from the print drive circuit to the heat generating element by the heat generation temperature of the heat generating element that generates heat due to the printing current supplied from the print drive circuit. Since the supplied printing current is adjusted, the temperature of the heating element during printing can be kept almost constant without the need for complex printing history control, resulting in uniform printing density and clear thermal printing. .

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is an enlarged sectional view of the main part of the thermal head, FIG. 2 is a plan view showing the overall structure of the thermal print head, and FIG. FIG. 3 is a circuit diagram for controlling the temperature of the heat generating resistance layer using a temperature sensor. DESCRIPTION OF SYMBOLS 1...Silicon substrate, 3...Print drive circuit section, 4...Heating resistance layer (heating element), 5...
...Diode (temperature sensor).

Claims (1)

[Claims] a print drive circuit unit that supplies a print current; a heating element that is arranged on a substrate and generates heat due to the print current from the print drive circuit unit; A thermal print head comprising a temperature sensor that adjusts the supplied printing current.