US3814897A - Thermal printing head - Google Patents

Thermal printing head Download PDF

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Publication number
US3814897A
US3814897A US00230332A US23033272A US3814897A US 3814897 A US3814897 A US 3814897A US 00230332 A US00230332 A US 00230332A US 23033272 A US23033272 A US 23033272A US 3814897 A US3814897 A US 3814897A
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United States
Prior art keywords
layer
printing head
thermal printing
opposite conductivity
semiconductor body
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Expired - Lifetime
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US00230332A
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English (en)
Inventor
H Otani
N Yukami
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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Publication date
Application filed by Matsushita Electric Industrial Co Ltd filed Critical Matsushita Electric Industrial Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material
    • B41J2/32—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material using thermal heads
    • B41J2/335—Structure of thermal heads
    • B41J2/34—Structure of thermal heads comprising semiconductors

Definitions

  • ABSTRACT A thermal printing head comprising a semiconductor body and a heat-generating resistive layer formed by diffusing an impurity into a surface portion of the semiconductor body by any suitable known method.
  • silicon having a low resistivity is employed to form the semiconductor body and an impurity having a conductivity opposite to that of the semiconductor body is employed to form the heat-generating resistive layer so as to completely concentr'ate current in the resistive layer and attain remarkable improvements in the heat generating characteristic of the thermal printing head.
  • This invention relates to a thermal printing head for use in a device which is adapted to print information on a heat-sensitive recording medium by means of thermal energy.
  • thermal printing heads of the kind in which head is generated by the concentrated flow of current through a resistor portion have been developed and are now available on the market.
  • the thermal printing heads of this kind can be broadly classified into two types.
  • a plurality of resistor portions are provided on-one end surface of a body of material having a high resistivity as an integral part of the body and current is passed through the resistor bank for generating heat in the resistor bank, while in the other type, a semiconductor such as silicon is used as a heatgenerating resistor and current is supplied to thisresistor through a supporting member supporting the resistor so as to cause generation of heatin the resistor.
  • the resistance of the body must be sufficiently higher than that of the heat-generating resistor portions.
  • an electrical insulator such as glass or ceramics is used as the material for the body, and a compound such as tin oxide is used to form the resistor portions.
  • the impurity concentration in a surface portion of the semiconductor body is selectively increased by a known method of selective diffusion or the like so as to reduce the resistance of the surface portion to a value extremely lower than that of the semiconductor body.
  • the thermal printing head of the latter type is appreciated in that the greater part of current can be concentrated in the surface portion doped with the impurity thereby generating substantial heat in such portion.
  • the present invention is featured by the fact that, in a thermal printing head comprising a semiconductor body and a heat-generating resistive layerformed by diffusing an impurity into a surface portion of the semiconductor body by any suitable known method, silicon having a low resistivity is employed to form the semiconductor body and an impurity having a conductivity opposite to that of the semiconductor body is employed to form the heat-generatin g resistive layer so as to completely concentrate current in the resistive layer and attain remarkable improvements in the heat generating characteristic of the thermal printing head.
  • FIGS. 1A and 1B are a perspective view and a longitudinal section respectively of a thermal printing head according to the present invention.
  • FIG. 2 is a perspective view of an array of thermal printing head chips made in accordance with the present invention.
  • FIGS. 3A to 3D show successive steps for the manufacture of the thermal printing head according to the present invention.
  • FIG. 4 is a graph showing variations in the resistivity of a semiconductor relative to temperatures.
  • a thermal printing head comprises a semiconductor body 11 of p-type or n-type silicon having a low resistivity.
  • a resistive layer I2 is formed in a surface portion including one end of the semiconductor body 11 by a known diffusion method and serves as a heat generating layer.
  • This resistive layer 12 is of the n-type and p-type when the semiconductor body 11 is of the p-type and n-type respectivelythereby forming a pn junction 15 therebetween.
  • a pair of electrodes 13 and 13' are in ohmic contact with the resistive layer I2 so that, when a voltage is applied across these electrodes 13 and 13', concentrated flow of current passes through the resistive layer 12 thereby generating substantial heat in the resistive layer 12.
  • a layer 14 of electrical insulator such as a silicon oxide film is formed on the semiconductor body 11 so as to prevent the electrodes 1 3 and 13 from contacting the surface portions of the semiconductor body 11 which are not doped with the impurity. Colors are produced on a heatsensitive sheet 16 at portions which are engaged by the hot head. It will be understood that such a thermal printing head can be constructed to have any desired size, and a plurality of thermal printing head chips of any suitable shape can also be arranged in an array as seen in FIG. 2. Referring to FIG. 2, a plurality of thermal printing head chips 18 are arranged in a line with an electrical insulator 17 interposed therebetween.
  • a semiconductor body 21 of silicon having a low resistivity is prepared at first as shown in FIG. 3A.
  • a perspective view and a side elevation of this semiconductorbody 21 are shown on the left-hand side and righthand side respectively of FIG. 3A.
  • This semiconductor body 21 is pre-formed to have a height h and a thickness w, which conform to the predetermined height and thickness of a thermal printing head to be finally produced.
  • substantial portions of the opposite side surfaces of the semiconductor body 21 are covered with an oxide f lm 23 except the end surface 22 and those surface portions lying within a suitable distance I measured from the end edges of the end surface 22.
  • This diffused layer 24 acts as a resistive layer.
  • a heat generating portion for applying thermal energy to a heatsensitive recording medium is preferably provided on a limited area, and in this respect, the provision of the 3 1 heat generating portion solely on the end surface 22 is essentially required as will be apparent from FlG. 1B.
  • the area of the surface portions covering the length 1 from the end edges of the end surface 22 is preferably as small as possible considering the fact that heat is wastefully lost in such portions. Therefore, the area of these surface portions should be limited to a minimum which is enough for electrical connection with the electrodes.
  • A' known method of vapor phase diffusion may be employed for the diffusion of the impurity.
  • An impurity such as phosphorus belonging to the group V is diffused when the semiconductor body of low resistivity is of the p-type, while an impurity such as boron belonging to the group lll is diffused when the semiconductor body is of the n-type. lt is needless to say that the resistance of the resistive layer can be controlled as desired by suitably diffusing the impurity.
  • a metal such as aluminum or nickel is deposited to provide a pair of electrodes 25 and 25' so as to extend over the oxide film 23 and over substantial portions of the diffused layer 24 on the side surfaces ofthe semiconductor body 21.
  • a method of vac-' uum evaporation may be employed for the deposition of the electrodes 25 and 25'.
  • the vacuum evaporation may be carried out while masking the end surface 22 so that the metal may not be deposited on the end surface 2 2, or after evaporating the metal on the entire surfaces, predetermined portions may be removed by photo-etching I and the electrode portions may be shaped to the desired form.
  • a cutting means such as a diamond cutter or wire saw may be used to cut the head into a size which has a width slightly larger than a predetermined width w
  • chemical etching is applied to the head for reshaping the pn junction 26, which has been impaired during the cutting operation, and adjusting the size of the head so that it has the predetermined width W2 v
  • the thermal printing head may be required to produce a temperature higher than, for example, 400 C depending on the kind of the heat-sensitive recording medium.
  • the heat generating characteristic of the head is necessarily deteriorated when a high temperature is produced due to the heat generated in the heat generating layer.
  • a high temperature can be satisfactorily produced without deteriorating the heat generating characteristic thereof for the reasons described below.
  • FIG. 4 shows the temperature characteristic of the lustrated by way of example, and the critical tempera ture becomes remarkably lower at a higher resistivity.
  • the critical temperatures of silicon crystals having respective resistivities'of 0.7 0cm, 1.3 Qcm, 4 flcm and 10 Om are ilheat is generated not only in the surface portion to be brought into contact with a heat-sensitive recording medium but also in the interior of the semiconductor body, and the heat generating efficiency of the thermal printing head is extremely lowered.
  • a resistive layer is formed in the surface portion of a semiconductor body of silicon by diffusing an impurity having a conductivity opposite to that of the semiconductor body so that the path of current is lim ited to one side of the pn junction and substantially all the current flows through the resistive layer.
  • the semiconductor need not have a high resistivity.
  • a large amount of heat is generated in the interior of the semiconductor body as is the case with the conventional head only when breakdown of the pn junction occurs to allow for flow of current into the interior of the semiconductor body.
  • the so-called secondary breakdown of a pn junction occurs only when a transition to the intrinsic region takes place in a semiconductor portion having a high resistivity.
  • the present invention is advantageous over the conventional thermal printing heads in that the path of current is limited to the resistive surface layer up to elevated temperatures and the head is free from any undesirable reduction in the heat generating efficiency up to such elevated temperatures.
  • a thermal printing head which generates heat for thermally recording information on a heat sensitive recording medium, comprising:
  • a body of low resistivity semiconductor material having a critical temperature at which a transition to the intrinsic region takes place which is higher than a color producing temperature of said heat sensitive recording medium;
  • a layer of opposite conductivity type from said semiconductor body formed on the surface of said body facing said heat sensitive recording medium, said layer extending over and part way down opposite sides of said body to form a semiconductor junction with said body;
  • each said electrode is disposed in ohmic contact with said opposite conductivity type layer.
  • a thermal printing head according to claim 2, wherein said opposite conductivity type layer comprises a doped impurity layer diffused into said semiconductor body.
  • a thermal printing head further comprising a plurality of said opposite conductivity type layers formed on said surface of said semiconductor body and a plurality of electrodes formed on said insulating layer and in contact with corresponding ones of said plurality of opposite conductivity type layers, each opposite conductivity type layer and its corresponding electrodes being separated from each other opposite conductivity layer and associated electrodes.
  • a printing head wherein said body of semiconductive material is composed of one of n-type and p-type materials.

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US00230332A 1971-03-04 1972-02-29 Thermal printing head Expired - Lifetime US3814897A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP1167571 1971-03-04

Publications (1)

Publication Number Publication Date
US3814897A true US3814897A (en) 1974-06-04

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Application Number Title Priority Date Filing Date
US00230332A Expired - Lifetime US3814897A (en) 1971-03-04 1972-02-29 Thermal printing head

Country Status (5)

Country Link
US (1) US3814897A (en:Method)
CA (1) CA953350A (en:Method)
DE (1) DE2210115C3 (en:Method)
FR (1) FR2127979A5 (en:Method)
GB (1) GB1389483A (en:Method)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3939325A (en) * 1972-12-01 1976-02-17 Matsushita Electric Industrial Co., Ltd. Thermal record printer head and method of making the same
US3967092A (en) * 1973-10-23 1976-06-29 Ing. C. Olivetti & C., S.P.A. Electrothermal print head
US4023184A (en) * 1975-10-06 1977-05-10 Mfe Corporation Thermal matrix type printing head
US4168505A (en) * 1978-10-04 1979-09-18 Atlan-Tol Industries, Inc. Stylus construction
US4194108A (en) * 1977-01-20 1980-03-18 Tdk Electronics Co., Ltd. Thermal printing head and method of making same
US4292641A (en) * 1979-03-24 1981-09-29 Josef Grassmann Electrically heated recording indicator for recording instruments and the like
US4523235A (en) * 1982-01-11 1985-06-11 Jan Rajchman Electronic microcopier apparatus
US5077564A (en) * 1990-01-26 1991-12-31 Dynamics Research Corporation Arcuate edge thermal print head
US5119111A (en) * 1991-05-22 1992-06-02 Dynamics Research Corporation Edge-type printhead with contact pads

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3161457A (en) * 1962-11-01 1964-12-15 Ncr Co Thermal printing units
US3609659A (en) * 1969-01-27 1971-09-28 Raymond Davis Thermal display unit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3161457A (en) * 1962-11-01 1964-12-15 Ncr Co Thermal printing units
US3609659A (en) * 1969-01-27 1971-09-28 Raymond Davis Thermal display unit

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3939325A (en) * 1972-12-01 1976-02-17 Matsushita Electric Industrial Co., Ltd. Thermal record printer head and method of making the same
US3967092A (en) * 1973-10-23 1976-06-29 Ing. C. Olivetti & C., S.P.A. Electrothermal print head
US4023184A (en) * 1975-10-06 1977-05-10 Mfe Corporation Thermal matrix type printing head
US4194108A (en) * 1977-01-20 1980-03-18 Tdk Electronics Co., Ltd. Thermal printing head and method of making same
US4168505A (en) * 1978-10-04 1979-09-18 Atlan-Tol Industries, Inc. Stylus construction
US4292641A (en) * 1979-03-24 1981-09-29 Josef Grassmann Electrically heated recording indicator for recording instruments and the like
US4523235A (en) * 1982-01-11 1985-06-11 Jan Rajchman Electronic microcopier apparatus
US5077564A (en) * 1990-01-26 1991-12-31 Dynamics Research Corporation Arcuate edge thermal print head
US5119111A (en) * 1991-05-22 1992-06-02 Dynamics Research Corporation Edge-type printhead with contact pads

Also Published As

Publication number Publication date
FR2127979A5 (en:Method) 1972-10-13
DE2210115B2 (de) 1974-08-15
CA953350A (en) 1974-08-20
GB1389483A (en) 1975-04-03
DE2210115C3 (de) 1975-03-27
DE2210115A1 (de) 1972-09-21

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