JPH0122154B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to improvements in thin film protective layers for thermal heads. More specifically, the present invention relates to a thermal head for a thermal printer used in a facsimile machine, etc., which has high hardness, excellent abrasion resistance, and excellent heat resistance, and can extend the life of the head. A thermal head 1 of a thermal printer conventionally used as one of the output methods for facsimiles, computer terminals, printers, recorders, etc. is basically constructed as shown in FIG. 1, for example. That is, a heat storage glaze layer 3 is provided on the substrate 2, a heat generation resistor layer 4 is formed on the heat storage glaze layer 3, and a pair of heat generation resistor layers 4 are formed on the heat storage glaze layer 3. Lead layers 51 and 53 are electrically connected. And as the top layer,
A protective layer 6 is provided to prevent the heating resistor layer 4 and lead layers 51, 53 from being worn out or damaged due to sliding contact with the thermal paper. Such a thermal head 1 has lead layers 51 and 53.
By supplying current to the heat generating resistor layer 4 through the heat generating resistor layer 4, the heat generating resistor layer 4 in the area of the gap between the lead layers 51 and 53 is made to generate heat, and this heat is transferred to the heat generating resistor layer 4 through the protective layer 6. Apply it to the thermal paper that will be in sliding contact,
A thermal recording is performed. In such a thermal head, the protective layer 6 includes:
It has high hardness, excellent abrasion resistance, and excellent heat resistance.As a result, even when subjected to continuous sliding contact with thermal paper over a long period of time and repeated heat generation over a long period of time, it remains stable. It is required to maintain the function sufficiently, for example, without causing deterioration of the resistance value of the heating resistor layer, and to maintain the life of the thermal head. Therefore, in view of these points, the present inventors
It has previously been proposed to use a thin film made of an amorphous phosphorus-boron compound having a composition of, for example, B ₁₃ P ₂ as a protective layer for a thermal head that exhibits favorable properties. The phosphorus-boron compound thin film proposed above has excellent wear resistance and heat resistance, and is useful as a protective layer for thermal heads. However, even this thin film has insufficient abrasion resistance and heat resistance under the extremely harsh usage conditions typical of thermal heads, which repeatedly generate heat over long periods of time under load due to sliding contact with thermal paper. I can't say it,
As the head is used for a long period of time, the characteristics of the head deteriorate, for example, the resistance value of the heating resistor layer deteriorates, and eventually the life of the thermal head ends, and further improvements in the characteristics of the protective layer are required. desired. The present invention was made in view of the above circumstances, and improves the characteristics of a phosphorus-boron compound thin film by adding a predetermined amount of a predetermined additive element.
The main object of the present invention is to provide a thermal head having a thin film protective layer that further improves its wear resistance and heat resistance, and further improves the life of the head when applied as a protective layer for the thermal head. The inventors of the present invention have conducted various studies for these purposes and have found that a predetermined amount of silicon as an additive element satisfies these purposes, leading to the present invention. That is, the present invention provides a thermal head having a heating resistor layer, a lead layer, and a protective layer on a substrate, in which the protective layer contains boron, phosphorus, and silicon, and has an atomic ratio of 1 to 1 boron. , the phosphorus content is
0.01 to 0.5, and moreover, the thermal head is characterized by containing silicon in an atomic ratio less than twice that of boron. Here, the protective layer used in the present invention contains phosphorus, boron, and silicon as essential components. In this case, the content of phosphorus is, in atomic ratio, boron 1
0.01 to 0.5. If it is less than 0.01, the effect of the present invention decreases. On the other hand, the upper limit of phosphorus content is 0.5,
If it exceeds this range, various problems will occur as a protective layer. Furthermore, more favorable results are obtained when the upper limit is 0.2, and from this point of view, the phosphorus content is
It is preferably 0.01 to 0.2. On the other hand, the content of silicon is greater than 0 and less than 2 to 1 boron in atomic ratio. In this case, if even a trace amount of silicon is included,
The protective film properties are improved compared to when silicon is not contained, and the effect becomes remarkable when the atomic ratio to boron is approximately 0.01 or more. Furthermore, when the silicon content is greater than 2, the protective film properties will be inferior to those without silicon, so the silicon content must be 2 or less. Note that the thin film protective layer having such a composition usually does not need to contain other additive elements, but in some cases, approximately 1% by weight may be added as necessary.
Ge, Sn, Pb, Al, Zr, Nb within the range below
etc. may be included. A protective layer with such a composition does not have a cubic or hexagonal single crystal structure like the well-known phosphorus-boron compounds, but is usually amorphous, and in some cases In some cases, they are polycrystalline. Moreover, the layer thickness is about 0.1 to 10 μm and is formed as a protective layer on a predetermined underlying device. To form such a protective layer on the thermal head, vapor phase epitaxy or sputtering can usually be used. In this case, when using the vapor phase growth method, the boron source is diborane (B ₂ H ₆ ), boron trichloride (BCl ₃ ), etc. as a volatile substance, and phosphine (PH ₃ ), phosphorus trichloride, etc. are used as volatile substances. (PCl ₃ ) or the like may be used as the phosphorus source, and silane (SiH ₄ ), silicon tetrachloride (SiCl ₄ ), or the like may be used as the silicon source. In addition,
When other additive elements are further included in the thin film protective layer, corresponding chlorides, hydrides, etc. may be used as the source. On the other hand, the flow rate ratio of each of these volatile substances can be easily determined through experiments depending on the desired thin film composition. On the other hand, H ₂ , He, Ar, etc. can be used as the carrier gas. The flow rate ratio, total flow rate, etc. of the carrier gas can also be determined through experiments as described above, and conditions depending on the composition may be used as appropriate. Note that the reaction temperature may generally be about 400 to 1300°C. On the other hand, when using sputtering, for example, each raw material powder is mixed according to the composition of the thin film protective layer, compression molded, and using it as a target,
RF sputtering may be performed according to a conventional method, such as performing RF sputtering in Ar under conditions of about 5 mTorr. In this way, a protective layer is formed on the thermal head by vapor deposition or sputtering. The thin film protective layer thus formed has high wear resistance and heat resistance, and significantly improves the life of the thermal head compared to a composition containing no silicon and/or phosphorus. In other words, it exhibits good protective layer performance even under harsh conditions of long-term use, and property deterioration such as resistance value deterioration of the heating resistor layer due to long-term use of the thermal head is significantly reduced, extending the life of the thermal head. becomes longer. In this case, one typical example of constructing a thermal head using the above-mentioned thin film protective layer will be described as follows. That is, referring to FIG. 1, the substrate 2 may be made of ceramic such as alumina. Furthermore, the glaze layer 3 provided on the substrate 2 may be formed from ordinary glass. Note that the glaze layer 3 is provided over almost the entire area on the substrate, as in the normal case, and its thickness is 15 mm.
The thickness may be 200 .mu.m, and it may be formed from a glass-containing paste or slurry by a conventional method such as screen printing or dipping. On the other hand, a heating resistor layer 4 is arranged on the glaze layer 3. The heating resistor layer 4 may be a thin film formed by various methods, but from the viewpoint of its characteristics, it is preferably a silicon polycrystalline thin film formed according to a known chemical vapor deposition method. preferable. Further, in this case, impurities such as P, As, B, etc. may be contained in the silicon polycrystalline thin film in an amount of about 100% by weight or less. And the resistance is approximately 2×10 ^-4 to 5×10 ^-3
It is sufficient if it is about Ω・cm. Furthermore, only one heating resistor layer 4 may be provided on the substrate in a predetermined shape, but usually, it is separated into a number of parallel strips and provided in a predetermined arrangement. , its thickness is generally 0.1 to 5 μm. A pair of lead layers 51 and 53 are connected to this heating resistor layer 4 having a predetermined shape and a predetermined arrangement. The lead layer may be formed as a thin film from various high-melting point metals according to various methods, but it is preferably formed from W or M ₀ or an alloy thereof, or a silicide thereof. In this case, the lead layer may be located below the heat-generating resistor layer, but it is usually preferable to laminate it above the heat-generating resistor layer. Moreover, the thickness is generally about 0.5 to 2 μm. Then, the above-mentioned thin film protective layer 6 is provided as the uppermost layer over almost the entire upper surface of such a laminate. A typical example of the thermal head of the present invention has been described in detail above, but in addition to this, in order to configure the thermal head, it is necessary to provide an intermediate layer that performs various functions, or to provide a layer that corresponds to the heat generating part on the substrate 2. It goes without saying that various aspects are possible, such as making the region convex. Moreover, the thin film protective layer can be formed into a multilayer structure of two or more layers, and the composition of each layer can be changed. The inventor conducted various experiments to confirm the effects of the present invention. An example is shown below. Experimental Example A thermal head as shown in FIG. 1 was constructed to confirm the effects of the present invention. First, the board 2 is 300 x 300 mm and 2 mm thick.
A glaze layer 3 with a thickness of 80 μm was formed on one surface of the alumina. Next, a 1 μm thick polycrystalline silicon film containing 1 wt% of B was deposited at 850°C using silane and diborane as sources and H ₂ as a carrier using chemical vapor deposition, and a 30 μm gap was formed using photolithography. Thus, a heating resistor layer 4 made of silicon in the form of parallel stripes with a width of 100 μm was formed. Thereafter, a W thin film with a thickness of 1.5 μm was deposited, and a window of 100×200 μm was formed in the center on each of the strip-shaped heating resistor layers 4 by photolithography. Then, W lead layers 51 and 53 were formed. Next, using a total of 14 types of thermal head 1 substrates formed in this way, a thin film protective layer belonging to the present invention or for comparison was formed on the entire surface with a thickness of 1 μm, and a total of 14 types of thermal head A were used. ~N was created. In this case, heads A and B are for comparison, using thin films made of a phosphorus-boron compound and containing no silicon, as previously proposed by the present inventors. In addition, heads C to D are for comparison using thin films made of boron and silicon. E to N are boron and silicon, or thin films made of boron, phosphorus and silicon, and among these, heads F, G, I, J and L are within the composition range of the present invention, on the other hand,
Heads E, H, K, M and N are outside the composition range of the present invention. On the other hand, a total of 14 kinds of thin film protective layers were formed according to the vapor phase growth method. That is, for each source, B ₂ H ₆ and PH ₃ are used for heads A and B,
B ₂ H ₆ and SiH ₄ were used for heads C, D, F, G, I, J and L, and B ₂ H ₆ and PH ₃ were used for heads E, H, K, M and N.
and SiH ₄ and H ₂ was used as the carrier gas. On the other hand, the reaction temperature was 900°C for heads A and B, and 800-900°C for heads C to N. Under these conditions, a total of 14 types of thin film protective layers with a thickness of 1 μm were formed on the base head by varying the flow rate ratio of each source, and the thin film composition was identified using an X-ray microanalyzer. As a result, it was confirmed that the composition was as shown in Table 1 below. Furthermore, the results of reflected electron beam diffraction confirmed that all 14 types of thin films were amorphous. For a total of 14 types of heads A to N obtained in this way, a diode matrix was constructed according to a known method, and a thermal paper was run in contact with it at normal pressure and running speed, and at intervals of 20 msec, for 1 m.
Pulse energization of sec was repeated. In this case, the energizing power is the amount required for the saturation density of the thermal paper, and pulse energization under such contact running conditions is repeated ¹⁰⁸ times, and the resistance value deterioration (%) of each heating resistor in each head is measured. , and averaged them to obtain the results shown in Table 1. In addition,
As a result of such a test, the resistance value of heads E, H, K, and M other than those of the present invention was infinite;
Furthermore, in the head N other than the one according to the present invention, a leakage current flowed through the surface of the protective layer even before the test, indicating a leakage state.

【table】

[Table] Shows that.
From the results in Table 1, heads F, G, I, J, and L using the thin film protective layer according to the present invention are different from heads A, B, using a phosphorus-boron compound thin film containing no silicon or phosphorus as the protective layer. Compared to C and D, the resistance value deterioration is significantly reduced,
It can be seen that the head life is getting longer.
In addition, heads E, H, using thin films other than those of the present invention,
From the results of K, M, and N, it can be seen that thin films having compositions outside the composition range of the present invention do not achieve the effects specified by the present invention.

[Brief explanation of the drawing]

FIG. 1 is a partially omitted sectional view showing one typical example of the configuration of a thermal head. Explanation of symbols 6...Thin protective layer.

Claims (1)

[Claims] 1. On the substrate, a heating resistor layer, a lead layer,
In the thermal head having a protective layer, the protective layer includes a boron layer, phosphorus and silicon, and the phosphorus content is 0.01 to 0.5 to 1 boron in an atomic ratio, and the phosphorus content is 2 to 1 boron in an atomic ratio. A thermal head characterized in that it contains less than twice as much silicon.