Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
1999-05-04
2001-03-13
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
Reexamination Certificate
active
06201558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thermal heads mounted in thermal printers or the like. The present invention particularly relates to a thermal head which can suppress voltage drop in a common electrode and can uniformly generate heat along an array of thermal head elements formed in the vicinity of the end of a substrate.
2. Description of the Related Art
In general, a thermal recording head mounted in a thermal printer includes an array of, or a plurality of arrays of, heating elements composed of heating resistors disposed on a substrate. When these heating elements are selectively energized in response to printing information, the heat generated by the elements colors a thermal recording sheet or melts and transfers ink on an ink ribbon onto plain paper or a transparent sheet.
FIG. 15
shows a conventional thermal head. A heat-insulating layer
112
composed of a glass glaze is formed over an entire heat dissipating substrate
111
composed of an electrically insulating ceramic such as alumina. A projecting section
113
which protrudes from the heat-insulating layer
112
is formed by etching or the like in the vicinity of the end
111
a
of the heat dissipating substrate
111
. A first common lead layer
114
a
with a thickness of approximately 1 &mgr;m is formed on the entire heat-insulating layer
112
by a sputtering process or the like. The first common lead layer
114
a
is composed of a hard, heat-resistant high-melting point metal, such as chromium, having high adhesiveness to the heat-insulating layer
112
. The first common lead layer
114
a
preferably has a large area and a large thickness of approximately 1 &mgr;m to reduce resistance thereof. Furthermore, a second common lead layer
114
b
is deposited on the entire surface of the first common lead layer
114
a
by a sputtering process. The second common lead layer
114
b
is composed of a cermet, which is a composite material of a metal and an insulating ceramic, such as Ta—SiO
2
(hereinafter, a Ta-containing cermet is referred to as a“Ta cermet”).
A strip antioxidative mask layer adjacent to the projecting section
113
is formed between the end
111
a
of the heat dissipating substrate
111
and the projecting section
113
of the heat-insulating layer
112
and on the second common lead layer
114
b
. The second common lead layer
114
b
is heated to approximately 700° C. so that the second common lead layer
114
b
is thermally oxidized over several thousands angstroms from the surface, except for the portion covered by the antioxidative mask layer. A first insulating interlayer
115
a
composed of oxide ceramic having significantly decreased defects is thereby formed.
The portion protected by the antioxidative mask layer remains as a conductive section
116
. The antioxidative mask layer is removed to expose the conductive section
116
on the first insulating interlayer
115
a.
A second insulating interlayer
115
b
composed of an insulating ceramic such as SiO
2
is deposited on the first insulating interlayer
115
a
by a sputtering process or the like, and then a contact hole
115
c
is formed in the second insulating interlayer
115
b
so that the conductive section
116
is exposed from the second insulating interlayer
115
b.
An underlying common electrode
117
a
composed of a high-melting point metal such as chromium is formed on the second insulating interlayer
115
b
so as to cover the conductive section
116
. An array of strip underlying discrete electrodes
118
a
composed of a high-melting point metal such as chromium is formed on the second insulating interlayer
115
b
. These underlying discrete electrodes
118
a
oppose the underlying common electrode
117
a
at a predetermined distance above the projecting section
113
.
A plurality of strip heating elements
119
composed of a Ta cermet is provided over the strip underlying discrete electrodes
118
a
and the underlying common electrode
117
a
. Thus, each heating element
119
forms a heating zone S
1
between the underlying common electrode
117
a
and the respective underlying discrete electrode
118
a.
Overlying discrete electrodes
118
b
composed of aluminum or copper are connected to the underlying discrete electrodes
118
a
through the heating elements
119
. The overlying discrete electrodes
118
b
extend to the other terminal end of the heat dissipating substrate
111
, away from the end
111
a
. Electrical power is supplied to each overlying discrete electrode
118
b
thorough the other terminal end.
An overlying common electrode
117
b
composed of aluminum or copper is formed on the strip heating elements
119
so as to oppose the underlying common electrode
117
a
. Furthermore, a protective layer
120
with a thickness of approximately 5 &mgr;m is deposited over the heating elements
119
, the overlying common electrode
117
b
, and the overlying discrete electrodes
118
b
other than the terminal section for an external circuit, by a sputtering process or the like. The protective layer
120
is composed of a material, such as sialon (a solid solution of a Si—Al—O—N compound), having high oxidation resistance and abrasion resistance.
These overlying discrete electrodes
118
b
are energized based on given printing information. A current from a overlying discrete electrodes
118
b
flows in the respective underlying discrete electrode
118
a
and the respective heating element
119
, and flows in the underlying common electrode
117
a
, the overlying common electrode
117
b
, the conductive section
116
, and the first and second common lead sublayers
114
a
and
115
b
toward the external circuit.
In a typical conventional thermal head including driver ICs, a glazed aluminum substrate is generally used in which a glass material is glazed on a heat dissipating substrate composed of alumina or the like. A plurality of linear heating elements is arranged in the vicinity of the end of the substrate. These heating elements are selectively energized according to recording information. The heat generated in the heating elements records dot images on thermal recording paper or plain paper by ink transfer from a thermal transfer ink ribbon provided between the thermal head and the plain paper.
FIGS. 16 and 17
are a cross-sectional view and a schematic plan view, respectively, of a main section of another conventional thermal head. A glass heat-insulating layer
202
is formed on a heat dissipating substrate
201
composed of an insulating ceramic such as glazed alumina. The heat-insulating layer
202
has a projection
202
a
having a trapezoidal cross-section at the end region. A first common lead layer
203
a
, which is composed of a high-melting point metal and has a thickness of approximately 1 &mgr;m, and a second common lead layer
203
b
, which is composed of a cermet of a high-melting metal and SiO
2
and has a thickness of approximately 1 &mgr;m, are formed on the heat-insulating layer
202
including the projection
202
a
by a sputtering process or the like. An antioxidative conductive metal such as MoSi
2
or antioxidative insulating ceramic such as SiO
2
with a thickness of approximately 0.2 &mgr;m is formed on the second common lead layer
203
b
by a sputtering process. The antioxidative material is etched to form a thermal-oxidation mask layer
204
with a predetermined pattern for providing contact holes by a photolithographic etching process.
The substrate
201
is heated to approximately 600° C. to 800° C. to form a first insulating interlayer
205
a
on the exposed region of the second common lead layer
203
b
which is not covered with the thermal-oxidation mask layer
204
, by thermal oxidation. A second insulating interlayer
205
b
composed of SiO
2
or the like is formed on the first insulating interlayer
205
a
. Such a double-layered configuration enhances reliability of interlayer insulation. A contact hole
205
c
is formed in the second insulating interlayer
205
b
at the position corresponding to the thermal-oxidation mask layer
2
Nakatani Toshifumi
Nanbu Tomonari
Sasaki Satoru
Shirakawa Takashi
Terao Hirotoshi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Tran Huan
LandOfFree
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