JPH1034931A - Thermal ink jet printing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently use heat generated by the heater in the injector of a printing head for thermal ink jet printer in the evaporation of liquid ink. SOLUTION: A heater 14 evaporating liquid ink is formed on a non-doped silicon substrate as a polysilicon layer and a heat insulating layer 24 containing either one of silicon dioxide and silicon nitride doped with either one of indium, lead, phosphorus, antimony, boron and arsenic is provided between the heater 14 and the substrate. A dopant destructs the lattice of the heat insulating layer 24 to lower the heat conductivity thereof. The heat generated in the heater 14 is suppressed in the diffusion to the substrate by the heat insulating layer 24 and liquid ink is efficiently heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head for a thermal ink jet printer, and more particularly to a heating means provided on the print head and a structure near the heating means.

[0002]

In current widespread ink jet printhead designs, the heater is formed as a resistor on the silicon chip surface. Although arranging the heater on the main surface of the chip in this manner is convenient for manufacturing the print head, there is a practical problem when the print head is used severely, for example, for high-speed printing or long-time printing. It is known to happen. In other words, only a part of the heat generated by the heater in the print head is used to eject the liquid ink from the print head, and about half of the heat generated by the heater is to directly heat the liquid ink. Instead, it is absorbed by the semiconductor chip and heats the entire chip. This is a waste of energy, and is particularly fatal in a very large print head used for printing a document having a pattern over the entire page width. Also, continuous heating of the printhead can significantly reduce the life of the printhead.

[0003] US Patent No. 5,264,874 discloses an ink jet printhead in which a number of thermoelectric conversion elements are formed on a substrate. Various semiconductor regions are formed in the substrate by diffusion of impurity atoms. According to the description of FIG. 5A and FIG. 5B, the impurities to be diffused include phosphorus, antimony, and arsenic.

[0004]

According to the present invention, there is provided a thermal ink jet printhead having at least one ejector. The ejector includes heating means defining a major surface configured to transfer heat to the liquid ink inside the printhead. A heat insulation layer is arranged adjacent to the heating means and on the side opposite the main surface. The heat insulating layer includes a material selected from the group consisting of silicon dioxide and silicon nitride. The material is doped with a dopant that breaks the lattice of the material.

[0005]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a greatly simplified perspective view of a part of an ejector for a thermal ink jet print head to which the present invention is applied. Although only one ejector is shown, an actual thermal ink jet printhead would include more than 100 ejectors as shown, and typically 300 to 600 ejectors per inch would be spaced apart. The structure of the ejector shown in FIG. 1 is a so-called side-shooter print head.
Known as ter printhead, a passage forming an ejector group is provided between two chips joined together. The print head includes a heater chip 10. The heater chip 10 is joined on its main surface to a so-called channel chip indicated by a dotted line 12. The design of the heater chip 10 is a semiconductor chip design known in the art, with an arbitrary number of heaters formed on its major surface as indicated by reference numeral 14. Normal,
One heater 14 is provided as a heating means for each ejector of the print head. A passage 16 is provided on the main surface of the heater chip 10 at a position facing each heater 14. This passage is formed as a groove in the channel chip 12. The channel chip 12 can be formed from any of metal materials, ceramics, and plastics known in the art. Heater chip 10 and channel chip 1
2, each passage 16 becomes a complete passage by the surface of the adjacent heater chip 10, and a heater surface is provided on the heater 14 inside the passage thus formed as shown in FIG.
Are arranged as shown in FIG.

FIG. 2 is a longitudinal sectional view taken along the line AA of FIG. 1 and shows in detail the layers that are integral to the actual heater 14 incorporating the present invention. As mentioned above, heater 14 is preferably a polysilicon layer that is doped and acts as a resistor. The heater 14 generates heat when voltage is applied, and the heat is transmitted from the surface of the heater to the liquid ink inside the print head.

Generally, in addition to a basic polysilicon layer, one or more protective layers for protecting the same are provided.
The protective layer prevents the heater 14 from being damaged or eroded by the liquid ink remaining in the passage 16 against the heater 14. A typical protective layer is a nitride layer 2
0 and a top layer 22 of sputtered tantalum. One or more of the plurality of protective layers may be formed on the same plane as the main surface of the substrate on which the heater chip 10 is formed, or may protrude upward from the main surface of the heater chip 10. May further be provided with an arbitrary number of planarizing layers (not shown) made of polyimide or the like. In a typical example of a thermal ink jet printhead, the heater 14 is provided in a small pit formed by a polyimide layer to increase vapor bubble formation efficiency.

In the present embodiment, a heat insulating layer 24 is provided between polysilicon forming the heater 14 and undoped silicon forming the majority of the substrate of the heater chip 10.
Is provided. Preferably, the heat insulating layer 24 functions only as a heat insulating layer, and is not electrically connected to each structure on the heater chip 10 at all. This thermal insulation layer 24 merely provides a region of lower thermal conductivity, which allows the heat generated by the heater 14 to flow in large quantities into the doped silicon which forms the majority of the heater chip 10. Can be prevented. Suitably, the thermal insulation layer 24 is comprised of a refractory material, preferably silicon dioxide or silicon nitride. This refractory material is doped with a dopant. Suitable dopants include indium, lead, phosphorus, antimony and arsenic. As described below, these dopants have an important effect in lowering the thermal conductivity of a heat-resistant material.

The thermal conductivity K of an insulator is theoretically expressed by the following equation.

K = (C _V V _S L) / 3 where C _V is the heat capacity of a unit volume specific to the material, V _S is the average speed of sound passing through the material, and L is the mean free path of phonons passing through the material.

Lattice normally found in silicon crystals, such as silicon dioxide, provides a convenient path for transmitting sound waves through the crystal. Those that scatter sound waves in the crystal shorten the mean free path of phonons propagating in the material and reduce the thermal conductivity K according to the above equation. Dopants such as phosphorus, lead, antimony, or arsenic introduced into silicon dioxide or silicon nitride become centers of phonon scattering in the lattice and reduce thermal conductivity. Similarly, thermal conductivity is also reduced by grain boundaries and the resulting non-uniformity of the material.

When doping silicon dioxide or silicon nitride with a dopant, it is better to avoid further formation of thermal carriers such as electrons or holes. A preferred doping level in the insulating layer 24 is 10% or 10%.
²⁰ / cm ³ or less.

The thickness of the heat insulating layer between the heater 14 and the undoped silicon of the heater chip 10 is less than 2 μm or 1 μm.
m. It has been found that the thermal insulation properties of the 0.5 μm thick thermal insulation layer 24 are similar to an undoped silicon dioxide layer approximately three times as thick.

In the above example, the heater chip 1 of the heat insulating layer 24
The area on the zero surface is almost the same as that of the heater 14, but the heat insulating layer 24 may extend beyond the boundary of the heater 14, or may be provided only on the lower side of a part of the heater 14.

Although the present invention has been described using the above structure,
The present invention is not limited to this embodiment, but can be modified and changed within the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a simplified perspective view of one of the ejectors that can be installed in a thermal inkjet printhead.

FIG. 2 is a longitudinal sectional view, taken along line AA of FIG. 1, showing the main parts of a heat-insulated heating element according to the invention.

[Explanation of symbols]

10 heater chips, 12 channel chips, 14 heaters, 24 heat insulating layers.

Continued on the front page (72) Inventor Sophie Buoy Bandeborake Pennfield Pineblock Circle, New York, USA 58

Claims (3)

[Claims] 1. A thermal inkjet printhead comprising at least one ejector, the ejector comprising: heating means defining a major surface configured to transfer heat to liquid ink within the printhead; A thermal insulation layer disposed adjacent to the means and opposite the major surface of the heating means and comprising a material selected from the group consisting of silicon dioxide and silicon nitride doped with a dopant that disrupts the crystal lattice; The printhead, wherein the dopant is selected from the group consisting of indium, lead, phosphorus, antimony, boron and arsenic. 2. The print head according to claim 1, wherein a ratio of the dopant in the heat insulating layer is 10% or less. 3. The printhead according to claim 1, wherein the heat insulating layer has no electrical holes.