CN1201933C - Heating resistor and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a heating resistor made of a non-metallic material capable of emitting heat when an electric current is applied, comprising at least tantalum (Ta), silicon (Si), oxygen (O) and nitrogen (N) as constituent elements . When the mol ratio of Si/Ta is 0.35<Si/Ta<0.80, the mol% of oxygen is 25mol%-45mol%, and the mol% of nitrogen is 5mol%-25mol%, the heating resistor has a resistance equal to or greater than 4mΩcm The resistivity, the peak angle of X-ray diffraction intensity is equal to or less than 37.5 degrees, and can withstand 100,000,000 pulses. A heating resistor having the above features is suitable for use in a print head of a thermal inkjet printer. In addition, the heating resistor has stable and high resistivity after annealing.

Description

Heating resistor and manufacturing method thereof

technical field

The present invention relates to a heating resistor and a method of manufacturing the heating resistor. More specifically, the present invention relates to a heating resistor having a stable high resistivity whose resistivity hardly shifts with heat while also exhibiting excellent cavitation resistance and a method of manufacturing the heating resistor , so it is suitable for use in thermal inkjet printers.

Background technique

Conventional heating resistors exhibit unstable resistivity under the influence of heat. More precisely, a resistor with a higher resistivity is more likely to exhibit an unstable resistivity. This unstable resistivity makes it difficult to control the resistor, especially when using the resistor's thermal energy.

Conventional heating resistors typically use the following elemental compositions: oxide; nitride; oxide/nitride; oxide/nitride/metal; oxide/nitride/metal/other, etc. Based on these compositions, many materials have been proposed. For example, Si-N-Ir-(Ru), Si-N-Ir-(Pt), Si-N-Ir-Ru-Pt, Si-O-Ir-(Ru), Si-O-Ir-(Pt ), Si-O-Ir-Ru-Pt, Si-C-Ir-(Ru), Si-C-Ir-(Pt), Si-C-Ir-Ru-Pt, etc.

Materials with the above composition do not help to reduce the resistivity change caused by heat. In other words, many situations that require the thermal energy of a heating resistor can no longer tolerate the resistivity change of conventional heating resistors.

In contrast, thermal inkjet printers are widely used, and many of them use heater resistors in their printheads. In thermal inkjet printers, a side shooter type print head and a roof shooter type print head are used. The side-firing type printhead ejects ink in a direction parallel to the heating surface of the heating resistor, while the top-firing type printhead ejects ink in a direction perpendicular to the heating surface of the heating resistor.

1A-1C are cross-sectional views schematically showing a side-firing type printhead, and FIGS. 1D-1F are cross-sectional views schematically showing a top-firing type printhead. As shown in FIG. 1A or 1D , the heating resistor is formed on the silicon substrate 1 , and the perforated plate 3 faces the silicon substrate 1 . Reference numeral 4 denotes a nozzle. In the side-firing type printhead, as shown in Figure 1A, the gap between the silicon substrate 1 and the perforated plate 3 forms nozzles 4 at their side ends, while as shown in Figure 1D, the nozzles 4 of the top-firing type printhead Formed above the heating resistor 2. In the above two structures, the heating resistor 2 is connected to an electrode (not shown), and the gap between the silicon substrate 1 and the perforated plate 3 forms an ink channel 5 for supplying ink.

Ink drops are ejected from the print head according to the following steps (1)-(5). (1) When a current representing image data flows through the heating resistor 2, the resistor 2 heats the ink layer to make it boil, so that a vapor core appears on the heating resistor 2 (FIG. 1B or 1E). (2) The steam cores gather together, thereby forming steam bubbles 6 . (3) As the steam bubble 6 expands, it pushes the ink 5-1 out of the nozzle 4, thereby forming an ink drop 5-2 at the tip of the nozzle 4, and the pressure of the steam bubble forces the ink drop onto the paper (Fig. 1C or 1F). (4) The steam bubble shrinks. (5) The steam bubble 6 is broken, and the resulting suction force draws out new ink for the next heating. The above steps (1)-(5) are completed in a very short time.

The effects produced by the above steps (1)-(3) are realized by film boiling. The phenomenon of film boiling typically occurs when a highly heated item is immersed in a liquid (such as iron quenching), or when the surface of an item in contact with a liquid is heated violently. Most inkjet printers utilize the latter genesis. As a result of film boiling, a pumping action occurs after bubble collapse. This suction effect is called cavitation.

Fig. 2A is a diagram schematically showing the step-by-step process from formation to collapse of steam bubbles. In this case, the heating resistor 2 is placed in an open pool with a depth of 1 mm. It takes 6 microseconds from steam bubble generation to collapse. FIG. 2A shows the vapor bubbles at microsecond intervals, while FIG. 2B shows the time control of the current applied to the heating resistor 2 .

As shown in FIG. 2B, it takes 1 microsecond for the current to flow through the heating resistor 2, whereby the heating resistor 2 heats the ink in the first stage of 1 microsecond. During the next 1 microsecond period, a vapor bubble appears, which pushes out the ink drop, and shrinks immediately before reaching the time of 3 microseconds. Once the steam bubble begins to shrink, the pressure inside the steam bubble will drop rapidly, and it will completely collapse in 6 microseconds. The pressure drop produces negative pressure cavitation shown by arrows a-1, a-2 and a-3 in Fig. 2A.

Negative pressure cavitation impacts heating resistor 2, pulling it upwards. If the depth of the above-mentioned open pool is 1 mm, the force to pull the heating resistor 2 upwards will reach 1000 ton/cm ² . In an inkjet printer, the heating resistor in the printhead is about 40 microns squared, so the impact force would be 16kg.

The heating resistor needs to have a resistivity sufficiently larger than a predetermined level. The predetermined level requires the lowest resistivity to emit the desired heat energy at the maximum current, and the high maximum current is tolerable in the circuit driving the heating resistor. The driving circuit and the heating resistors are arranged on the same board in a monolithic type print head, and the maximum current of the transistor of the driver in this type of print head is about 100 mA. In this case, the required resistivity is equal to or greater than 4 mΩcm. Typically, such a large resistivity is not possible with metal resistors.

A heating resistor required for thermal inkjet printers should meet the following conditions: (1) Resistivity - not the typical resistivity that metal resistors have, that is to say a large resistivity equal to or greater than 4mΩcm, more preferably equal to or greater than 5mΩcm . (2) Stability against heat - the rate of change in resistivity due to heat is equal to or less than 0.05%/°C, more preferably close to 0%/°C. (3) Cavitation resistance - withstand 100,000,000 pulses in the open cell test.

For resistivity, if the maximum current of the driver transistor is about 100mA, and the power per pulse is 1W, the required resistance value is 100Ω. Most heating resistors are metal resistors, so typical resistivities are equal to or less than 1 mΩcm.

Thermal inkjet printers typically use square heater resistors. If the resistivity of the resistor is equal to or less than 1 mΩcm, a square heating resistor of about 100 nm in thickness is required to emit the desired heat energy. 100nm thick is too thin for a resistor to have a long lifetime.

Materials with a composition of Ta-Si-O or the like are known to be suitable materials for heating resistors because they have relatively excellent characteristics. However, the lifetime of heating resistors made of these materials cannot reach the desired level at a resistivity of 4 mΩcm. More precisely, a heating resistor cannot withstand 100,000,000 pulses in an open cell test with water. To make matters worse, the thermally induced resistivity change rate was 0.05%/°C, which was still larger than the allowable level.

Under the above conditions, a heating resistor made of Ta-Si-O material requires a protective film when used in an inkjet printer. The protective film protects the heating resistor from ink corrosion and damage from cavitation. Covering the heating resistor with a protective film about 1 micron thick hinders the heat energy emitted by the resistor. Because such output loss requires more energy, conventional Ta-Si-O heating resistors can hardly meet the requirement of energy saving.

invention disclosure

An object of the present invention is to provide a heating resistor which has high resistivity, low rate of change by heat, and excellent cavitation resistance, and thus is suitable for use in thermal inkjet printers.

The above objects are achieved by a heating resistor which emits heat energy when an electric current is applied.

The heating resistor (12) includes at least tantalum (Ta), silicon (Si), oxygen (O), and nitrogen (N) as constituent elements.

The heating resistor thus constituted is suitable for use in thermal inkjet printers because it exhibits stable high resistivity like non-metallic materials, but has little change in resistivity due to heat, and has excellent thermal resistance like metallic materials. Anti-cavitation.

In this heating resistor, the mol% (M2) of nitrogen is 5mol%≤M2≤25mol%. In this case, the mol ratio of Si/Ta is 0.35<Si/Ta<0.80, and the mol% (M1) of oxygen is 25mol%≤M1≤45mol%.

In the above setting, only the Si/Ta mol ratio of 0.35<Si/Ta<0.80 can be selected, and in addition only the oxygen mol% (M1) of 25 mol%≤M1≤45 mol% can be selected.

The heating resistor may include an amorphous structure in which a broad peak angle of X-ray intensity appearing in X-ray diffraction is 37.5 degrees and a resistivity is equal to or greater than 4 mΩcm.

In addition, the heating resistor may include an amorphous structure in which the light absorption coefficient is 70000/cm or less at light energy of 0.5-1 eV, and the resistivity is equal to or greater than 4 mΩcm.

The heating resistor (12) may be used in the printhead of an inkjet printer. In this case, the heating resistor (12) may directly contact the ink and generate air bubbles in the ink. Therefore, the printhead of the thermal inkjet printer has higher energy efficiency for better droplet output as well as excellent cavitation resistance.

Another object of the present invention is to provide a method of manufacturing a heating resistor having high resistivity, low rate of change by heat, and excellent cavitation resistance, and thus suitable for use in thermal inkjet printers.

The above method is achieved by a method of manufacturing a heating resistor (12) which generates heat when an electric current is applied thereto, said method comprising the following steps:

forming a thin film (12) made of Ta-Si-O-N on the substrate (11); and

A heating resistor (12) is formed by annealing the Ta-Si-O-N film.

In the above method, annealing may be performed in air. In this case, the annealing step can be easily performed.

In the above method, annealing may be performed in an inert gas. In this case, the electrode film can be prevented from being oxidized during the annealing, so that problems caused by oxidation do not occur.

If the heating resistor is used in a printhead of a thermal inkjet printer, the temperature during annealing may be 350-600°C.

If the print head of the thermal inkjet printer is a monolithic type where the print head and the driving circuit are mounted on the same silicon substrate, the temperature during annealing may be 350-450°C.

In the above method, annealing may be performed for 10-30 minutes.

The Ta-Si-O-N film may have a protective film (21) thereon. In this case, the Ta-Si-O-N thin film can be annealed while having a protective film thereon, and the annealing can be performed in air. Therefore, oxidation of electrode films and the like can be prevented.

Brief description of the drawings

The above objects, as well as other objects and advantages of the present invention, will become more apparent upon reading the following detailed description and accompanying drawings, in which:

1A, 1B and 1C are diagrams schematically showing ink ejection step by step, respectively, for explaining the operating principle of a conventional side jet type print head;

1D, 1E and 1F are diagrams schematically representing ink ejection step by step, respectively, which are used to explain the operating principle of a conventional top ejection type print head;

Figure 2A is a graph schematically showing the bubble formation process observed every 1 microsecond in the open cell experiment, while Figure 2B is a graph showing that the current is controlled by the time passed in the heating resistor in the open cell experiment:

3 is a cross-sectional view schematically showing a heating zone and surrounding structures in a print head of a thermal inkjet printer according to an embodiment of the present invention;

Figure 4 is a table of composition and resistivity of three typical heating resistor samples;

Fig. 5 is a graph for explaining the basis of the present invention, showing the relationship between the resistivity of Ta-Si-O thin films and Ta-Si-Al-O thin films having different composition ratios and the peak angle appearing after X-ray diffraction. relation;

Figure 6 is a graph showing the X-ray diffraction results of one of the Ta-Si-O-N materials;

Figure 7 is a graph showing the relationship between the peak angle and the resistivity of the Ta-Si-O-N material and the Ta-Si-O and Ta-Si-Al-O materials shown in Figure 5 after X-ray diffraction;

FIG. 8 is a graph showing the relationship between resistivity and temperature of a Ta-Si-O-N thin film for comparison with conventional techniques;

9 is a graph showing the light absorption characteristics of a Ta-Si-O-N thin film formed on a silicon substrate;

Figure 10 is a graph showing the results of multiple heating resistors made from Sample 1 shown in Figure 4 in an open cell experiment;

Figure 11 is a graph showing the results of multiple heating resistors made from Sample 2 shown in Figure 4 in an open cell experiment;

Figure 12 is a table listing the results of closed cell experiments using Sample 2 as well as the results of open cell experiments;

Fig. 13 is a table listing 11 kinds of Ta-Si-O-N film samples with different composition ratios, including samples 1-3 shown in Fig. 4 and other samples 4-11;

Figure 14 is a graph showing the relationship between the peak angle and resistivity of Samples 1-11 obtained by adding the results of Samples 4-11 to the graph shown in Figure 7;

Figure 15 is a graph showing the change in resistivity of annealed Ta-Si-O-N films and non-annealed films;

16 is a graph showing SST (Stress Increase Experiment, Step-up Stress Test) results of an annealed heating resistor and a non-annealed heating resistor;

17 is a cross-sectional view schematically showing a structure near a heating region in a print head of a thermal inkjet printer according to an embodiment of the present invention;

18A, 18B and 18C are sectional views explaining step by step the manufacturing method of the print head of the thermal inkjet printer shown in FIG. 17;

Figure 19 is a graph showing the relationship between the annealing temperature and the increase rate of surface resistivity after annealing under 4 different conditions; and

Fig. 20 is a graph showing the relationship between the annealing treatment time and the relative resistivity after annealing under 4 different conditions.

Best Mode for Carrying Out the Invention

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

Fig. 3 is a cross-sectional view schematically showing a print head, particularly a heating zone and its surrounding structure. The print head 10 shown in FIG. 3 is a so-called top-firing type print head. A component not shown in the print head 10 is an oxide layer (SiO ₂ ) having a thickness of 1-2 μm, which is formed on the surface of the substrate 11 .

Reference numeral 12 denotes a heating resistor film made of at least four constituent elements Ta (tantalum), Si (silicon), O (oxygen) and N (nitrogen), which are formed on an oxide layer by a thin film formation technique. The heating resistor film 12 is patterned by photolithography to have a stripe shape. Finished electrode films made of gold etc. also have striped sheets. Strip-shaped pieces of electrode film are deposited on the heating resistor film 12 such that a pair of electrode pieces cover both ends of one piece of heating electrode film 12 , thereby exposing the central portion of each piece of heating electrode film 12 . When forming the electrode film, a shield layer made of Ti—W is formed such that the shield layer is interposed between the electrode film and the heating resistor film 12 . The exposed area of the heating resistor film 12 , that is, the area not covered by the electrode film, serves as the heating area 13 . Of each pair of electrode sheets, one electrode sheet will serve as the individual electrode 14 and the other will serve as the common electrode 15 .

After the heating zone 13 is formed, an organic material such as polyimide is coated on the substrate 11 as a to-be-wall layer with a thickness of about 20 microns. The pattern of the prewall layer is formed by photolithography so that the layer remains on the individual electrodes 14, and the substrate 11 is cured, wherein the substrate 11 is exposed to heat at a temperature of 300-400° C. for 30-60 minutes. A wall 16 made of photosensitive polyimide is thus formed on the individual electrode 14 with a height of approximately 10 micrometers.

After forming the heating zone 13 and the walls 16, an apertured plate 17 is deposited on the substrate 11 as a top layer. The apertured plate 17 is then etched (dry etched) using a metal mask (not shown) to form nozzles 18 in the apertured plate 17 on the heating zone 13 . The nozzles 18 are spaced relatively small, for example about 40 microns. Since the apertured plate 17 is formed on the wall 16, the apertured plate 17 and the common electrode 15 are separated from each other. A distance of 10 microns in height (which is the same as the height of the wall 16 ) serves as the ink passage 19 . Ink is supplied into the space above the heating zone 13 via the ink passage 19 .

As shown in FIG. 3, the heating zone 13 is exposed, in other words, there is no protective layer or the like thereon. A protective layer is usually used in this type of printhead and has a thickness of not less than 1 micron. A structure without a protective layer greatly improves energy efficiency for ink ejection.

As described above, the constituent elements of the heating resistor film 12 are at least Ta, Si, O, and N. A preferable range of elemental composition is as follows. The molar ratio of Si/Ta is 0.35<Si/Ta<0.80, more preferably 0.35<Si/Ta<0.45. M1 (mol% of oxygen) is 25mol%≤M1≤45mol%. M2 (mol% of nitrogen) is 5mol%≤M2≤25mol%.

The heating resistor film 12 has the following properties: an amorphous structure; an angle at which the X-ray intensity peaks is equal to or less than 37.5 degrees; a resistivity equal to or greater than 4 mΩcm; and an optical absorption coefficient at 0.5-1 eV of less than 70000/cm.

The heating resistor according to the present invention is characterized by having a 4-element composition including Ta, Si, O and N. This structure is an advanced structure based on the conventional composition Ta-Si-O, which shows relatively excellent performance for heating resistors. The above 4-element composition is the result of testing samples with various Ta-Si-O and other element compositions in experiments.

Fig. 4 shows a table of compositions of typical 3 samples having a 4-element composition and which are experimental items for the test. As shown in Fig. 4, the constituent elements of the sample are Ta, Si, O and N. The table shows the mol% of each element, the mol ratio of Si/Ta, the mol% of O+N, and the resistivity (mΩcm).

Since the results shown in this table have tolerances, the sum of the mol% of the 4 elements is not exactly 100%. That is, the total mol% of the sample is as follows. Sample 1: 100.1%, Sample 2: 99.7%, and Sample 3: 100.6%.

Fig. 5 is a graph explaining the characteristics of the 4-element heating resistor of the present invention. The figure shows the characteristic lines, which represent the relationship between the peak angle 2θ and the resistivity after X-ray diffraction of the eight samples, respectively. The samples include 6 materials composed of Ta-Si-O and 2 materials composed of Ta-Si-Al-O, which have different composition ratios. θ represents the reflection angle of the Bragg reflection, and the peak angle represents the angle of the broad peak of the X-ray diffraction intensity. In this graph, the horizontal axis represents the peak angle 2θ (degrees), and the vertical axis represents the resistivity (mΩcm) in logarithmic order.

Line "a" represents the characteristics of 6 samples composed of Ta-Si-O, while line "b" represents the characteristics of 2 samples composed of Ta-Si-Al-O. Both line "a" and line "b" show that there is a correlation between peak angle 2θ and resistivity. Through these experiments, the peak angle 2θ decreases with increasing oxygen. The inventors of the present invention investigated this phenomenon as follows.

The above-mentioned broad peaks are generally exhibited in materials with an amorphous structure. The appearance of such broad peaks is a reflection of the structure factor (reciprocal space), which represents the order of the closest atoms. For example, the structure factor of a three-element (A, B and C) compound as a whole is the sum of 6 structure factors A-A, A-B, B-B, A-C, B-C and C-C. Fourier transformation of the structure factors of a compound yields the average atomic order therein.

Therefore, the peak angle reflects the average atomic order. That is, as shown in FIG. 5, the peak angle 2θ is related to the resistivity. From this fact and the relationship between the amount of oxygen and the peak angle 2θ, the inventors of the present invention deduced that the peak angle may reflect positive and negative ions (oxygen) (such as Ta-O, Si-O, and Al-O) The average interatomic distance and configuration of . This inference further suggests that the average interatomic distance of Ta-Ta and Ta-Si also depends on the oxygen density, so the peak angle also reflects the average interatomic distance of Ta-Ta and Ta-Si.

This inference is consistent with the results shown in Figure 5. In Figure 5, the points representing the Ta-Si-Al-O sample scatter as the resistivity decreases along the characteristic line "a" (bottom right in the figure). This fact is demonstrated by the fact that the lower the resistivity, the greater the effect of the sequence among positive ions, since the number of negative ions decreases with decreasing resistivity.

Therefore, the peak angles obtained in X-ray diffraction reflect the connections between the closest atoms. This fact suggests that the peak angle may reflect the strength and cavitation resistance of the heating resistor. In addition, resistivity has the potential to reflect the band structure of the sample, that is, the connections between atoms.

The inventor also noted the fact that the characteristic lines "a" and "b" are not parallel to each other. More precisely, as the peak angle 2θ increases (closer to the right end of the figure), the characteristic line "b" (Ta-Si-Al-O) exhibits a larger Resistivity (on top of graph).

This fact may be due to the fact that the number of bonds of Al is smaller than that of Si and Ta. In this case, Si is a tetravalent atom, Ta is a pentavalent atom, and Al is a trivalent atom. Based on this inference, the inventors focused on elements that change the number of valence bonds. In fact, it has been observed that as the Si increases in the Ta-Si-O material, the resistivity also increases. This fact indicates that Si-rich materials tend to have greater resistivity with increasing peak angle.

The inventors considered the compositions Ta-Si-O and Ta-Si-Al-O as combinations of positive and negative ions, namely, (Ta-Si)-O and (Ta-Si-Al)-O, and derived the following inference.

In addition, if the number of valence bonds of atoms in the material is smaller, it exhibits higher resistivity. Furthermore, because electrons in materials with high resistivity are localized at peak angles equal to or less than 37.5 degrees (a range not typical in metal resistors), the chemical linkages in the materials are likely to be strong. This fact indicates that the material has a higher cavitation resistance.

The inventors also observed that the rate of change (temperature coefficient) of resistivity with heating is small in materials with small peak angles.

From the above facts, materials with high resistivity and small peak angle are suitable for the heating resistor of the present invention. Typical heating resistors made of metal have a small thermal change in resistivity, but never have a high resistivity suitable for a heating resistor. The inventors then deduced that non-metallic materials are likely to have smaller peak angles and higher resistivities.

In addition, the preferred material should have other anion elements ((Ta-Si)-(O-β)), because it is obvious from the characteristic line "b" ((Ta-Si-Al)-O), that for (Ta -Si-α)-O material, when the peak angle 2θ is small, it is difficult to increase the resistivity to 4mΩcm. If nitrogen with a bond number of minus 3 is used as an anion element, the material exhibits high resistivity because the bond number of oxygen is minus 2. It suggests that when the peak angle 2Θ is equal to or less than 37.5 degrees (a range not typical for metallic materials), the material will have a resistivity equal to or greater than 4 mΩcm. Based on the above deduction, the inventors prepared a thin film made of a material composed of Ta-Si-O-N by DC sputtering in a mixed atmosphere of Ar, O and N, in which stripe targets of Ta and Si were sputtered.

Sputtering was performed under the following conditions. Final pressure: 0.5 × 1.33 × 10 ^-4 Pa, sputtering power: 1 kW, film formation rate: 2.4 nm/min, where one Si substrate was used for analysis and the other was used for pulse resistance in the same chamber Receptivity experiments with a 1 µm _SiO2 layer on the latter substrate.

After annealing the Ta-Si-O-N film thus formed, the properties of the stabilized heating resistor such as resistivity, rate of change of resistivity by heating are stable, that is, they do not change with time.

Fig. 6 is a graph showing the results of X-ray diffraction analysis of the Ta-Si-O-N film (sample 3 in Fig. 4). The figure shows an X-ray diffraction intensity pattern with a single broad peak, which represents that the film has an amorphous structure. The unit of the X-ray diffraction intensity is an arbitrary unit.

FIG. 7 is a graph showing the relationship between the peak angular position and resistivity of three Ta-Si-O-N sample films having different composition ratios as shown in FIG. 4 . The figure also shows characteristic line "a" (Ta-Si-O) and characteristic line "b" (Ta-Si-O-N) for reference. As is apparent from this figure, the results of the three samples involved are in the region where the peak angle is equal to or less than 37.5 degrees and the resistivity is equal to or greater than 4 mΩcm. This result indicates that these materials are suitable for use as heating resistors in thermal inkjet printers.

The composition ratios of the three samples shown in FIG. 4 were obtained by analyzing the heating resistor film on the Si substrate by RBS (Rutherford reflectance spectroscopy). Because RBD hardly detects lighter nitrogen, the nitrogen content in Samples 1 and 2, which have relatively low nitrogen contents, was detected with ESCA (Electron Spectroscopy for Chemical Analysis), which is a type of photoelectron spectroscopy.

FIG. 8 is a graph showing the relationship between the resistivity and temperature of the heating resistor (Ta-Si-O-N) of Sample 2 in FIG. 4 . The figure also shows the relationship of two conventional materials (Ta-Si-O). In this figure, the characteristic line "d" represents the relationship of sample 2, while the characteristic line "e" represents the result of a conventional Ta-Si-O heating resistor with a resistivity of 4mΩcm at room temperature, and the characteristic line "f" Representative results for another conventional Ta-Si-O heating resistor whose resistivity at room temperature is 2 mΩcm. The horizontal axis of the graph represents temperature (° C.), while the vertical axis represents the ratio of resistivity “R(room temperature)” at room temperature to change resistivity “R(T)” at temperature T.

These materials are formed on a silicon substrate in the same measurement chamber. The profile of the material is the same as for the open cell experiments described above. Each Ta-Si-O-N heater resistor film is 40 square microns.

Resistivity is obtained by measuring the voltage applied across a heating resistor through which current flows. Measure the voltage with a digital voltmeter. The temperature changes with the current. Measure the temperature with an infrared emitting thermometer, which measures the temperature over a small area. As shown in Figure 8, the resistivity change rate of the Ta-Si-O-N heating resistor, represented by the characteristic line "d", is 10% (0.025%/°C) at 400°C, and the resistivity is equal to or greater than 5mΩcm . Conversely, conventional materials represented by characteristic lines "e" and "f" have a change rate of resistivity upon heating that is 2 times or more greater than that of characteristic line "d".

FIG. 9 is a graph showing light absorption characteristics of a Ta-Si-O-N heating resistor film formed on a silicon substrate. The inventors of the present invention focused on the light absorption characteristics to observe the characteristics of Ta-Si-O-N heating resistor films from different angles. This graph shows the light absorption coefficient, and the obtained coefficient is obtained from the light transmission of the sample having the same composition ratio as the sample 2 shown in FIG. 4 and having an arbitrary thickness.

The horizontal axis of the graph shown in FIG. 9 represents light energy (eV), while the vertical axis thereof represents light absorption coefficient (cm ⁻¹ ). According to the graph, the absorption coefficient obtained is small (equal to or less than 70000/cm) in the energy range of 0.5-1eV, and the absorption coefficient gradually increases in the high-energy region of 1eV or more energy. It is evident from Figure 9 that the resulting absorption coefficient is not close to 0 and there is no apparent light gap.

The light absorption features shown generally indicate the presence of a band gap. That is, the heating resistor made from Sample 2 in FIG. 4 is similar to a degenerate semiconductor because of the optical characteristics and small temperature coefficient (change rate of resistivity by heating equal to or less than 0.025%/°C). In other words, the heating resistor is similar to a degenerate semiconductor in which the energy distribution of carriers (free electrons or holes) is a degenerate Fermi distribution.

Open cell experiments were then performed to evaluate cavitation resistance. In this experiment, a Ta-Si-O-N material formed on an oxidized silicon substrate in which the sample 1 shown in FIG. W-Ti film and Au film are then patterned.

The prepared heating resistor used in the open cell experiment is 25 square micrometers, and the thickness is 480 micrometers. A pulse with a frequency of 10 kHz and a pulse width of 1 microsecond is applied across the heating resistor. Frequency and pulse width were determined based on the ink output performance of an inkjet printhead using a prototype heating resistor fabricated under the same conditions.

FIG. 10 is a graph showing the results of an open pool experiment for a sample formed in the same chamber as Sample 1 shown in FIG. 4 . The horizontal axis of the graph shown in FIG. 10 represents the number of applied pulses, and the vertical axis thereof represents the resistance value (Ω). As shown in FIG. 10, none of the nine heating devices (ch00-ch64) produced disconnection after 100,000,000 pulses were applied, that is, excellent results were obtained. In addition, no apparent damage was observed with an electron microscope after the experiment.

FIG. 11 is a graph showing the results of an open tank experiment for another sample formed in the same chamber as that used to form sample 2 shown in FIG. 4 . Like FIG. 10, the horizontal axis of the graph shown in FIG. 11 represents the number of applied pulses, while the vertical axis represents the resistance value (Ω). Figure 11 shows what happens when a pulse is applied to the sample until the wire breaks. In the 9 heating devices (ch00-ch64), as shown in FIG. 11, the line disconnection was found for the first time after applying the pulse 200,000,000 times.

As we all know, the open cell test is one of the most severe tests, which is an almost destructive test. The ability of the heater resistor to withstand 100,000,000 pulses indicates that the heater resistor has the long-lasting durability required for an inkjet printer.

As shown in FIG. 4 , samples 1 and 2 having excellent cavitation resistance had a resistivity of 5 mΩcm or more. This is much higher than the average required for heating resistors in inkjet printheads.

The inventors of the present invention also built another prototype printhead to actually prove their theory. This prototype was fabricated from materials in the same chamber as Sample 2. The nozzles of the prototype printhead were formed in an apertured plate formed in the wall. The print head was made to output water and ink, whereby the damage of the heating resistor made of Sample 2 was observed from the viewpoint of anti-cavitation. This experiment is called a closed cell experiment as opposed to an open cell.

Figure 12 is a table showing the results of closed cell experiments and open cell experiments (Sample 2, using water). Regardless of the protective film structure, the heating resistor made of sample 2 can withstand 200,000,000 pulses in the open cell test and 1,000,000,000 pulses in the closed cell test. These results were on target (100,000,000 pulses in the open cell experiment and 1,000,000,000 pulses in the closed cell experiment).

If ink (black ink) is used, the applied pulses are limited to about 300,000,000 times due to damage to the material rather than to the heating resistor. However, the heating resistors were observed immediately after the experiment and no damage was found.

It was thus demonstrated that the heating resistor film having the composition of Ta-Si-O-N exhibits excellent characteristics for use in a print head of an inkjet printer. The inventors of the present invention also produced several kinds of Ta-Si-O-N resistor films whose composition ratios were different from each other to find out the preferable composition ratio.

FIG. 13 is a table in which characteristic elements, resistivity, open cell experiment results, and peak angles of composition ratios of samples 1-11 (samples 1-3 are shown in FIG. 4 ) are listed. The composition ratios of the other materials (samples 4-11) were different from each other in the above-mentioned experiments according to the experience of the inventors.

Of the 11 materials, samples 7, 10 and 11 failed the pulse resistance test. Because they cannot withstand 100,000,000 pulses, they are not suitable as heating resistors for thermal inkjet printers. Among the materials that did not pass the test, some characteristic elements such as mol% of O, mol% of N, and Si/Ta ratio have very large or very small values (the crossed part in the table ),.

A preferable value range which is an excellent characteristic of the heating resistor is determined as follows based on the material which passed the pulse resistance test and other tests. The mol% (M1) of O is 25mol%≤M1≤45mol%, the mol% (M2) of N is 5mol%≤M2≤25mol%, and the mol ratio of Si/Ta is 0.35<Si/Ta<0.80.

Figure 14 is a graph made from the graph shown in Figure 7 (relationship between peak angle and resistivity), but also showing characteristic results for samples 4-11. In this figure, the black dots represent the results for materials that passed the pulse resistance test, while the white dots represent the results for materials that did not pass the pulse resistance test.

The above description related to FIGS. 5 and 7 shows that the region bounded by a peak angle equal to or less than 37.5 degrees and a resistivity equal to or greater than 4 mΩcm is preferable for the heating resistor. However, Figure 14 shows that all Ta-Si-O-N materials (samples 1-11) are within this range. That is, even samples 4, 10, and 11, which did not pass the pulse resistance test, were within this range. Therefore, the range suggested by the preferred material is not suitable for evaluating the durability such as cavitation resistance and the like of a heating resistor in a thermal inkjet printer.

The resistivity of the Ta-Si-O-N heating resistor film changes with time. These changes in resistivity have the potential to affect the reliability and design of products using the heating resistor. However, if it is Ta-Si-O-N made by sputtering, it is already known that annealing can stabilize resistance characteristics (such as resistivity, rate of change of resistivity by heating) according to experiments.

Therefore, annealing is an important step in fabricating stable Ta-Si-O-N resistor films. A method for forming a Ta-Si-O-N heating resistor film by annealing will be described in detail below.

Sputtering was performed by a sputtering apparatus under the following conditions. Target: Ta plate including a predetermined amount of Si (for example, Ta:Si=3:1), pressure: equal to or lower than 1.33×10 ⁻⁴ Pa, process gas: a predetermined amount of Ar, substrate temperature: about 200° C., And layer formation rate: about 2 nm/sec.

A Ta-Si-O-N film was formed to a thickness of 480 nm on a Si substrate which was thermally oxidized by the above-mentioned sputtering. As mentioned above, the thus formed material has an amorphous structure, which was confirmed by X-ray diffraction. Without annealing, the material will have a resistivity that changes over time.

FIG. 15 is a graph showing the change in characteristics between annealed and non-annealed films. The material used for comparison was sample 4 shown in FIG. 13, and its composition ratio was: 42.0% Ta, 16.0% Si, 30.0% O, and 12.0% N. In this case, annealing was performed at 400° C. in the atmosphere.

The horizontal axis of the graph represents the logarithm of time to represent longer periods of time, while the vertical axis represents resistivity change. The change in resistivity on the vertical axis is a relative change. In this case, 100 represents the initial resistivity (at 1 on a logarithmic scale for easy understanding) immediately after layer formation, which is taken as a reference value. In this figure, the black circles (line "h") represent the results for the non-annealed material, while the black square points (line "g") represent the results for the annealed material.

As shown by line "h", the resistivity of the non-annealed material increases with time. Conversely, the resistivity of the annealed material increases by 20-30% due to annealing, but the line "g" exhibits a constant resistivity over time.

The annealed resistive film is further tested by Auger electron microscopy to find the oxide film or oxygen distribution. This test showed that the annealing did not produce an oxide film or oxygen distribution because only a 3-5 nm thick (which is 0.1% of the film thickness) native oxide film was found throughout the test. This fact suggests that the reason for the increase in resistivity upon annealing is not due to oxidation reaction.

To investigate the characteristic differences between annealed and non-annealed films, pressure increase experiments (SST) were performed in an open cell. The materials used for the SST were formed under almost the same conditions as those used to form Sample 4 shown in FIG. 13 .

Figure 16 is a graph showing SST results for annealed and non-annealed materials. The horizontal axis of the graph represents the energy (μJ) of the applied pulse (2 μsec pulse at 10 kHz), while the vertical axis thereof represents the rate of change (%) of the resistivity. In this case, the thickness of the annealed film was 360 nm, and the thickness of the non-annealed film was 700 nm. Both the annealed and non-annealed films were 25 microns square. In this figure, the black circle dots in line "i" represent the results for annealed films, while the black square dots in line "j" represent the results for non-annealed films.

The energy range of the applied pulses was set at approximately 1.2-5 μJ. 1.2 μJ is the minimum level required to form an air bubble that pushes out the ink drop, and 5 μJ is the point at which the material (heating resistor film) fades, ie the film is no longer able to withstand the pressure. The initial resistivity was set as a reference resistivity indicating the rate of change in resistivity. Thicker films are generally stronger, all else being equal. However, thicker non-annealed films exhibit greater rates of resistivity change at the point of material fading.

The range between the dashed lines k and m (2 μJ-3 μJ) represents the actual range of ink jetting. In this range, the range of resistivity variation for the annealed material (line "i") is stable, while the range of resistivity variation for the non-annealed material (line "j") is unstable (decreases, then slightly increases).

According to the change with time shown in Fig. 15 and the results in practical use, annealing the formed Ta-Si-O-N film is a very effective factor for producing a stable film.

The above-mentioned annealing heating resistor film is formed through the following steps. Perform sputtering (target: Ta plate including Si, vacuum pressure: 1.33×10 ^-4 Pa or less, substrate temperature: 200°C, process gas: Ar, layer formation rate: 2nm/sec), form an electrode layer, and form an electrode layer and the pattern of the heating resistor, and then the heating resistor was annealed (at 400° C. for 10 minutes in the atmosphere).

The electrode for driving the heating resistor according to the above-described embodiment of the present invention has a double-layer structure of a W-Ti film and an Au film (not shown in FIG. 3 ). Since the electrode layer is formed over the heating resistor film, the electrode layer should make good contact with the heating resistor film. However, Au films suitable for electrode layers are difficult to bond on Ta-Si-O-N. The W-Ti film of the electrode layer was used as a base film to connect the Au film and the resistor film because the W-Ti film can bond Au and Ta-Si-O-N well.

In a state where the electrodes are exposed to the ink, electrolysis caused by a short-circuit current may occur in the ink because the ink is a weak electrolyte. Electrolysis has the potential to form additional air bubbles that block ink flow.

To avoid electrolysis, the electrodes should be coated with an insulating film. An oxide insulating film such as Ta-Si-O is preferable.

FIG. 17 is a diagram showing the structure of an insulating film according to another embodiment of the present invention. In this embodiment, the heating area 13 of the heating resistor 12 is also coated with an insulating film. As mentioned above, the Ta-Si-O-N heating resistor film without protective film has excellent cavitation resistance, but the coating structure as shown in Fig. 17 is necessary for higher cavitation resistance rather than higher energy The case of efficiency is preferred.

As shown in FIG. 17, the heating zone 13, the individual electrode 14, and the common electrode 15 shown in FIG. 3 are all covered with a protective film 21 made of Ta—Si—O. 18A-18C are sectional views explaining step by step the method of forming the heating device shown in FIG. 17 . 18A-18C show the structure of electrodes (individual electrode 14 and common electrode 15) in detail.

As shown in FIG. 18B, the electrode has a three-layer structure including a lower adhesive film 22 of W-Ti, an electrode film 23 of Au, and an upper adhesive film 24 of W-Ti. The electrode and heating area 13 of these structures are covered with an insulating protective film 21 made of Ta-Si-O material, which has excellent cavitation resistance.

The upper adhesive layer 24 is used to bond Au and Ta—Si—O, thereby firmly connecting the Au electrode film 23 and the Ta—Si—O protective film 21 . Therefore, the heating means is isolated from the ink.

The steps of forming the heating device on which the insulating protective film is formed will be described in detail with reference to FIGS. 18A to 18C.

First, the lower adhesive film 22, the electrode film 23, and the upper adhesive film 24 are deposited on the heating resistor film 12 already deposited on the substrate 11 (FIG. 18A). Then, the lower adhesive film 22, the electrode film 23, and the upper adhesive film 24 are patterned to form the heating area 13, individual electrodes 14, and common electrodes 15 (FIG. 18B). The heating resistor film 12 is then patterned to form a heating device.

The next step should be annealing, but annealing the heating resistor film 12 in the atmosphere while bringing the upper adhesive film 24 of W-Ti into contact with the electrode film 23 will generate an oxide layer on the upper adhesive film 24 . More precisely, the oxygen in the air becomes free atoms during annealing due to the high temperature under the above-mentioned conditions. The free atoms oxidize the surface of the upper adhesive film 24 . Since it is difficult to bond the oxide layer thus formed on the Ta-Si-O protective film 21, the W-Ti upper adhesive film 24 cannot function to connect the protective film 21 and the electrode film 23.

The following conditions for annealing were set to avoid the formation of an oxide layer.

Annealing is first performed in an inert gas to avoid the formation of free oxygen. Inert gas is a generic name representing a low-reactivity gas, such as group 0 elements He, Ar, Kr, Xe, and Rn (rare gases), and _N2 gas. In this embodiment, N ₂ gas and Ar gas are used.

The steps and specific conditions are as follows.

(1) A Ta-Si-O-N heating resistor film is formed.

(2) A lower adhesive film (W-Ti) is formed.

(3) An electrode film (Au) is formed.

(4) Forming an upper adhesive film (W-Ti).

(5) Patterning of the electrode layer (W—Ti, Au, W—Ti).

(6) Patterning the heating resistor film.

(7) Annealing the heating resistor film.

Atmosphere: _N2 gas (inert gas)

Temperature: 350-450°C

Processing time: 10-30 minutes

(8) An oxide insulating film (Ta-Si-O) is formed.

(9) The oxide insulating film (Ta-Si-O) is patterned.

According to the method described above, the upper adhesive film 24 is not oxidized because the annealing is performed in _N2 gas.

Since the W-Ti upper adhesive film 24 is not oxidized, the Ta-Si-O oxide insulating film 21 is firmly formed on the upper adhesive film 24, and thus the Ta-Si-O insulating film 21 and the Au electrode are realized. Strong connection between membranes 23.

The same procedure can be used when annealing is performed in Ar gas.

Another method is to perform annealing in a vacuum chamber. In this case, the vacuum chamber is a sputtering chamber for sputtering, so annealing is performed continuously after the heating resistor is formed by sputtering. Annealing in a vacuum chamber is achieved by radiant heat. The method described above prevents free oxygen from contacting the upper adhesive film 24 .

Annealing may be performed after forming the Ta-Si-O oxide insulating film in order to prevent free oxygen from contacting the upper adhesive film 24 . In this case, annealing may be performed in the atmosphere (air).

The steps and conditions used in this method are as follows.

(1) A Ta-Si-O-N heating resistor film is formed.

(2) A lower adhesive film (W-Ti) is formed.

(3) An electrode film (Au) is formed.

(4) Forming an upper adhesive film (W-Ti).

(5) Patterning of the electrode layer (W—Ti, Au, W—Ti).

(6) Patterning the heating resistor film.

(7) An oxide insulating film (Ta-Si-O) is formed.

(8) The oxide insulating film (Ta-Si-O) is patterned.

(9) Annealing the heating resistor film.

Atmosphere: Air (atmosphere)

Temperature: 350-450°C

Processing time: 10-30 minutes

Figure 19 is a graph showing the resistivity increase rate of a heating resistor film that has been annealed but under different atmospheric conditions: atmospheric (air) (indicated by black circles), _N2 gas (indicated by black triangles). Indicated), Ar gas (indicated by a white triangle), and air used after forming a Ta-Si-O oxide insulating film and forming a pattern (hereinafter referred to as "air with a protective film) (indicated by a crossed line). The figure The horizontal axis of represents the annealing temperature (° C.), and the vertical axis represents the sheet resistivity increase rate of the heating resistor film. In this case, the treatment time for annealing was 10 minutes.

As shown in Fig. 19, in the temperature range of 200-400°C, the increase rate of the sheet resistivity increases linearly regardless of the atmosphere conditions. Then, after the temperature exceeds 400 °C, the increase rate decreases slowly. The resistivity itself continues to increase even as the rate of increase decreases. This result suggests that the resistivity stabilization effect of annealing depends only on heat, not on atmospheric conditions.

When used in a thermal inkjet printer, the heating resistor should be annealed at at least 350°C because the heating resistor releases heat equal to or greater than 300°C when driven in the printer. In other words, if the resistor is annealed at a temperature equal to or lower than 300°C, the effect of annealing does not appear. When the temperature is lower or higher than 400°C, the higher the annealing temperature, the smaller the change rate of resistivity. Figure 19 clearly reflects this fact. In this graph, when the temperature is equal to or higher than 400°C, the rate of increase becomes smaller and smaller. However, it is known that an annealing temperature exceeding 600° C. also impairs cavitation resistance. In a monolithic structure, where the heating resistor and its driving circuit are mounted on the same silicon substrate, the maximum annealing temperature is limited to 450°C, because "400°C for 1 hour" is the limit for the diffusion layer of the LSI on the silicon substrate. value. Therefore, the annealing temperature range for the heating resistor used in the monolithic type thermal inkjet printer should be 350-450°C.

Fig. 20 is a graph showing the relationship between the annealing time and the relative resistivity of the annealing resistance film under the same different atmosphere conditions as those shown in Fig. 19, the horizontal axis of the graph represents the annealing time (minutes), and the vertical axis represents Relative resistivity, where 100 represents the initial resistivity. In this case, the annealing temperature was 400°C.

As shown in Fig. 20, the resistivity increases sharply during the first 4 minutes from the start of annealing regardless of the atmospheric conditions. Then, the resistivity increased slowly until the 10th minute. The resistivity is stable over a period of 10 minutes to 30 minutes.

Therefore, the preferred treatment time for annealing is 10-30 minutes. In other words, the lower limit should be set at 10 minutes, where the sharp increase in resistivity stops, and the upper limit should be set at 30 minutes, where the resistivity is stable.

As described above, the resistivity of the Ta-Si-O-N heating resistor film is stabilized by annealing. The effect of annealing does not depend on the difference in atmosphere. In addition, the effect of annealing does not change even when the heating device is covered. This fact allows the heating device to have a protective layer thereon to prepare a highly reliable print head for thermal inkjet printers. In this case, the annealing should be performed in an inert gas or after forming the protective film to prevent the bonding layer between the heating device and the protective layer from being oxidized, thereby firmly adhering the protective film to the heating device.

Various embodiments and modifications can be made without departing from the spirit and scope of the invention.

For example, the heating resistor of the present invention is not only made of Ta, Si, O, and N, but may also include other elements such as hydrogen and the like.

The heating resistors of the present invention are not limited to use in thermal inkjet printers. The heating resistor of the present invention can also be used, for example, in inkjet printers using the piezoelectric effect, or any products other than inkjet printers.

The above-mentioned embodiments are only used to illustrate the present invention, not to limit the scope of the present invention. The scope of the invention is shown by the appended claims rather than by the embodiments described above. Various modifications can also be made in the equivalent replacement of the claims of the present invention, and should be regarded as within the scope of the present invention in the claims.

This application is based on Japanese Patent Application No. H11-133306 filed on May 13, 1999, and Japanese Patent Application No. 2000-67612 filed on March 10, 2000, and includes specification, claims, drawings and abstract . The contents of the above-mentioned Japanese patent application are hereby incorporated by reference.

Claims (12)

1, a kind of heating resistor that is used for the printhead of ink-jet printer, this resistor sends heat energy when applying electric current, and produces bubble when the contact ink,

Described heating resistor (12) comprises that Ta, Si, O and N are as component at least, and wherein the mol% of N is M2, and the span of M2 is 5mol%≤M2≤25mol%.

2, heating resistor as claimed in claim 1, wherein, the mol of Si/Ta ratio is 0.35＜Si/Ta＜0.80.

3, heating resistor as claimed in claim 2, wherein, the mol% of O is M1, the span of M1 is 25mol%≤M1≤45mol%.

4, heating resistor as claimed in claim 1, wherein, the mol% of O is M1, the span of M1 is 25mol%≤M1≤45mol%.

5, heating resistor as claimed in claim 1, wherein, described heating resistor (12) directly contacts ink.

6, make the method for the heating resistor of claim 1, this heating resistor (12) is used for the printhead of temperature-sensitive ink-jet printer, said method comprising the steps of:

Go up the film that formation is made by Ta-Si-O-N in substrate (11), this film comprises that Ta, Si, O and N are as component at least, and wherein the mol% of N is M2, and the span of M2 is 5mol%≤M2≤25mol%; And

By forming heating resistor (12) at the described Ta-Si-O-N film of 350-600 ℃ annealing temperature.

7, method as claimed in claim 6, wherein, annealing is to carry out in air.

8, method as claimed in claim 6, wherein, annealing is to carry out in inert gas.

9, method as claimed in claim 6, wherein, the described printhead of temperature-sensitive ink-jet printer is the printhead of monolithic type, wherein printhead is installed on the identical silicon base with drive circuit, and annealing during temperature 350-450 ℃.

10, method as claimed in claim 6, wherein, annealing was carried out 10-30 minute.

11, method as claimed in claim 6, wherein, described Ta-Si-O-N film has diaphragm (21) thereon.

12, method as claimed in claim 11, wherein, described annealing is to carry out in air.

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