MXPA06007798A - Combined material layering technologies for electric heaters - Google Patents

Abstract

A layered heater is provided that comprises a dielectric layer formed by a first layered process, a resistive layer formed on the dielectric layer, the resistive layer formed by a second layered process, and a protective layer formed on the resistive layer, wherein the protective layer is formed by one of the first or second layered processes or yet another layered process. The first layered process is different than the second layered process in order to take advantage of the unique processing benefits of each of the first and second layered processes for a synergistic result. The layered processes include, by way of example, thick film, thin film, thermal spraying, and sol-gel. Additional functional layers are also provided by the present invention, along with methods of forming each of the individual layers.

Description

STRATIFICATION TECHNOLOGIES OF COMBINED MATERIALS FOR ELECTRIC HEATERS FIELD OF THE INVENTION The present invention is generally concerned with electric heaters and more particularly with methods for forming individual layers of a stratified electric heater.

BACKGROUND OF THE INVENTION Laminated heaters are commonly used in applications where space is limited, when heat output needs vary across the surface, where a rapid thermal response is desirable or in ultra-clean applications, in where moisture or other contaminants can migrate to conventional heaters. A stratified heater generally comprises layers of different materials, ie an electrical material and a resistive material, which are applied to a substrate. The electrical material is first applied to the substrate and provides electrical insulation between the substrate and the electrically active resistive material and also reduces current leakage to ground during operation. The resistive material is applied to the electrical material in a predetermined pattern and provides a resistive heater circuit. The stratified heater also includes conductors connecting the resistive heater circuit to a source of electrical power, which is commonly cycled by a temperature controller. The conductor to resistive circuit interface is also commonly mechanically and electrically resistive of the foreign contact by providing voltage relief insulation and electrical insulation by means of a protective layer. Thus, stratified heaters are highly adaptable for a variety of heating applications. Stratified heaters can be "thick" film, "thin" film or "thermally atomized" among others, wherein the main difference between these types of stratified heaters is the method in which the layers are formed. For example, layers for thick film heaters are commonly formed using processes such as screen printing, decal application or film assortment heads, among others. Layers for thin film heaters are commonly formed using deposition processes such as ion deposition, sputtering, chemical vapor deposition (CVD) and physical vapor deposition (PVD), among others. Still another series of processes other than the thin technique and thick profile are those known as thermal atomization processes, which may include by way of example, flame atomization, plasma atomization, wire arc atomization and HVOF high-speed oxygen), among others. With thick film laminated heaters, the type of material that can be used as the substrate is limited due to the incompatibility of the thick film laminated processes with certain substrate materials. For example, stainless steel 304 for high temperature applications is without a compatible thick film dielectric material due to the relatively high thermal expansion coefficient of the stainless steel substrate. Thick film dielectric materials that will adhere to this stainless steel are more commonly limited in temperature than the system can withstand before (a) the dielectric becomes unacceptably "conductive" or (b) the dielectric is de-layered or otherwise impaired of performance degradation. Additionally, the processes for thick film laminated heaters involve multiple stages of drying and high temperature heating for each coating within each of the dielectric elements, resistive element and protective layers. As a result, the processing of a thick film laminated heater involves multiple processing sequences. Similar limitations exist for other stratified heaters that use thin film and thermal atomization processes. For example, if a resistive layer is formed using a thermal atomization process, the pattern of the resistive element must be formed by a subsequent operation such as laser etching or water jet sculpting, unless a process such as in masking is used of shadow, which often results in imperfect resistor patterns. As a result, two stages of separate processes are required to form the resistive layer pattern. Accordingly, each of the processes used for the stratified heaters have inherent disadvantages and inefficiencies compared to other processes.

BRIEF DESCRIPTION OF THE INVENTION In a preferred form, the present invention provides a stratified heater comprising a dielectric layer formed by a first stratified process, a resistive layer formed on the dielectric layer, the resistive layer formed by a second stratified process and a layer protective layer formed on the resistive layer, wherein the protective layer is formed by one of the first or second stratified processes or still another stratified process. The first stratified process is different from the second stratified process in order to take advantage of the unique processing benefits of each of the first and second stratified processes for a synergistic result. The stratified processes include, by way of example, thick film, thin film, thermal atomization and sol-gel. In another form, a stratified heater comprising a first layer formed by a layered process is promoted, a second layer formed on the first layer, wherein the second layer is formed by a stratified process different from the stratified process of the first layer. The layers are additionally selected from a group of functional layers consisting of a link layer, a graduated layer, a dielectric layer, a resistive layer, a protective layer, a coating layer, a detector layer, a connection plane layer. to ground, an electrostatic layer and an RF layer, among others. Additionally, a layered heater comprising a substrate, a link layer formed on the substrate, a dielectric layer formed on the link layer and a resistive layer formed on the dielectric layer is provided. The dielectric layer is formed by a first stratified process and the resistive layer formed by a second stratified process. Similarly, a stratified heater comprising a substrate, a graduated layer formed on the substrate, a dielectric layer formed on the graduated layer and a resistive layer formed on the dielectric layer is provided. The dielectric layer is formed by a first stratified process and the resistive layer formed by a second stratified process. In still another form, there is provided a laminated heater comprising a substrate, the dielectric layer formed by a first layered process, a resistive layer formed on the dielectric layer, the resistive layer formed by a second layered process and a protective layer formed on the resistive layer, where the protective layer is formed by a stratified process. In another form, a coating layer is formed on the protective layer and the coating layer is also formed on a layered process. The first stratified process is different than the second stratified process in order to take advantage of the unique processing benefits of each of the first and second stratified processes for a synergistic result. According to a method of the present invention, a stratified heater is formed by the steps of forming a first layer by a first layered process and forming a second layer on the first layer by a second layered process. The first and second layers are preferably a dielectric layer and a resistive layer, respectively and another protective layer is formed on the resistive layer according to another method of the present invention.

The first stratified process is different than the second stratified process.

BRIEF DESCRIPTION OF THE FIGURES The present invention will be more fully understood from the detailed description and the attached figures, in which: Figure 1 is a side view of a layered heater constructed in accordance with the principles of the present invention; Fig. 2 is an enlarged partial cross-sectional view taken along line A-A of Fig. 1, of a laminated heater constructed with the principles of the present invention; Figure 3a is an enlarged partial cross-sectional view of a stratified heater having a tie layer constructed in accordance with the principles of the present invention; Figure 3b is an enlarged partial cross-sectional view of a stratified heater having a graduated layer constructed in accordance with the principles of the present invention; Figure 3c is an enlarged partial cross-sectional view of a stratified heater having a tie layer and a graduated layer constructed in accordance with the principles of the present invention; Figure 4 is a graph illustrating the transition of CTE from a substrate to a dielectric layer in accordance with the principles of the present invention; Figure 5 is an enlarged partial cross-sectional view of a stratified heater having a coating layer constructed in accordance with the principles of the present invention; Figure 6 is an enlarged partial cross-sectional view of a stratified heater having a plurality of resistive layers constructed in accordance with the principles of the present invention; Figure 7a is an enlarged partial cross-sectional view of a stratified heater having a protective layer constructed in accordance with the principles of the present invention; Figure 7b is an enlarged partial cross-sectional view of a stratified heater having a ground shield layer constructed in accordance with the principles of the present invention; Figure 7c is an enlarged cross-sectional view of a stratified heater having an electrostatic shield constructed in accordance with the principles of the present invention; Figure 7d is an enlarged partial cross-sectional view of a stratified heater having an RF shield constructed in accordance with the principles of the present invention and Figure 8 is an enlarged cross-sectional view of a stratified heater having a discrete component Embedded constructed in accordance with the principles of the present invention. Corresponding reference numbers indicate corresponding parts in all the various views of the figures.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The following description of the preferred embodiments is exemplary only by nature and is not intended in any way to limit the invention, its application or uses. Referring to Figures 1 and 2, a heater laminated in accordance with a form of the present invention is illustrated and indicated generally by reference number 10. The laminated heater 10 comprises a number of layers arranged on a substrate 12, wherein the substrate 12 may be a separate element disposed next to the part or device to be heated or the substrate 12 may be the part or device itself. As best shown in Figure 2, the layers preferably comprise a dielectric layer 14, a resistive layer 16 and a protective layer 18. The dielectric layer 14 provides electrical insulation for the substrate 12 and the resistive layer 16 and is formed on the substrate 12. in a thickness commensurate with the power output, applied voltage, proposed application temperature or combinations thereof, of the layered heater 10. The resistive layer 16 is formed on the dielectric layer 14 and provides a heater circuit for the layered heater 10 , thereby providing heat to the substrate 12. The protective layer 18 is formed on the resistive layer 16 and is preferably an insulator, however other materials such as an electrical or thermally conductive material can also be used in accordance with the requirements of a specific heating application as long as it remains within the scope of this i nvention Additionally, the stratified heater 10 is shown in a generally cylindrical configuration with a spiral resistive circuit, however, other configurations and circuit patterns may also be used as long as they remain within the scope of the present invention. As further shown, the terminal blocks 20 are preferably disposed on the dielectric layer 14 and are in contact with the resistive layer 16. Thus, the electrical conductors 22 are in contact with the terminal blocks 20 and connect the resistive layer 16 to an energy source (not shown). (Only one terminal block 20 and one electrical conductor 22 are shown for clarity and it should be understood that two terminal blocks 20 with an electrical conductor 22 per terminal block 20 is the preferred form of the present invention). The terminal blocks 20 are not required to be in contact with the dielectric layer 14 and thus the illustration of the embodiment of Figure 1 is not intended to limit the scope of the present invention, as long as the terminal blocks 20 are electrically connected to the resistive layer 16 in some form. As further shown, the protective layer 18 is disposed on the resistive layer 16 and is preferably a dielectric material for electrical insulation and protection of the resistive layer 16 from the operating environment. Additionally, the protective layer 18 can cover a portion of the terminal blocks as long as there is sufficient area to promote an electrical connection to the power source. Preferably, the individual layers of the stratified heater 10 are formed by different layered processes in order to take advantage of the benefits of each process for a global synergistic result. In one form, the dielectric layer 14 is formed by a thermal atomization process and the resistive layer 16 is formed by a thick film process. By using a thermal atomization process for the dielectric layer 14, an increased number of materials such as the substrate 12 that would otherwise be incompatible with the thick film application of the dielectric layer 14 can be used. For example, 304 stainless steel for a high temperature application can be used as the substrate 12, which can not be used with a thick film process due to the maladjustment or excessive mismatch of the coefficient of thermal expansion (CET) between this alloy and the possible thick film dielectric glasses. It is generally known and understood that the CTE characteristics and insulation resistance property of thick film glasses is inversely proportional. Other compatibility issues may arise with substrates having a low temperature capacity, for example plastics and also with a substrate comprising a thermally treated surface or other property that could be adversely affected by the high temperature heating process associated with the thick films. Additional substrate materials 12 may include, but are not limited to, copper coated with nickel, aluminum, stainless steel, low carbon steels, tool steel, refractory alloys, aluminum oxide, and aluminum nitride. When using a thick film process, the resistive layer 16 is preferably formed on the dielectric layer '14 using a film print head in a form of the present invention. The manufacture of the layers using this thick film process is shown and described in U.S. Patent No. 5,973,296, which is assigned in common with the present application and the contents of which are hereby incorporated by reference in their entirety. Additional thick film processes may include, by way of example, screen printing, spraying, lamination and transfer printing, among others. The terminal blocks 20 are also preferably formed using a thick film process in a form of the present invention. Additionally, the protective layer 18 is formed, using a thermal atomization process. Accordingly, the preferred form of the present invention includes a thermally atomized dielectric layer 14, a thick film resistive layer 16 and terminal blocks 20 and a thermally atomized protective layer 18. In addition to the increased number of compatible substrate materials, it is The present invention has the additional advantage of requiring only one heating sequence to cure the resistive layer 16 and the terminal blocks 20, instead of multiple heating sequences that would be required if all the layers were formed using a stratified process of thick film. With only one heating sequence, the. The selection of resistor materials is widely expanded. A typical thick film resistive layer must be able to withstand the temperatures of the heating sequence of the protective layer, which will often determine a higher heating temperature resistor. By enabling the selection of a lower heating temperature resistor material, the interfacial stresses between the high expansion substrate and the lower expansion dielectric layer have been reduced, thus promoting a more reliable system. As a result, the stratified heater 10 has broader application and is manufactured more efficiently in accordance with the teachings of the present invention. In addition to using a thermal atomization process for the dielectric layer 14 and the protective layer 18 and a thick film process for the resistive layer 16 and the terminal blocks 20, other combinations of layered processes can be used for each of the layers individual as long as they remain within the scope of the present invention. For example, Table I below illustrates possible combinations of laminate processes for each of the layers within the stratified heater.

Table I Accordingly, a variety of combinations of laminate processes can be used for each individual layer, according to specific heater requirements. The processes for each layer as shown in Table I should not be construed as limiting the scope of the present invention and the teachings of the present invention are that different layered processes for different functional layers within the stratified heater 10. Thus, a First stratified process is used for a first layer (eg thermal atomization for dielectric layer 14) and a second layered process is used for a second layer (eg thick film for resistive layer 16) according to the principles of the present invention. Thermal atomization processes may include, by way of example, flame atomization, plasma atomization, wire arc atomization HVOF (high speed oxygen fuel), among others. In addition to the film print head as described above, the thick film processes may also include, by way of example, screen printing, spraying, lamination and transfer printing, among others. Thin film processes can include ion deposition, sputtering, chemical vapor deposition (CVD) and physical vapor deposition (PVD) among others. Thin film processes such as those disclosed in U.S. Patents 6,305,923, 6,341,954, and 6,575,729, which are incorporated herein by reference in their entirety, may be used with the heater system 10 as described herein as long as they remain within the scope of the present invention. With respect to the sol-gel processes, the layers are formed using sol-gel materials. In general, sol-gel layers are formed using processes such as immersion, centrifugation or painting, among others. Thus, as used herein, "stratified heater" should be interpreted to include heaters comprising functional layers (e.g., dielectric layer 14, resistive layer 16, and protective layer 18, among others as described in greater detail later in the specification). present), wherein each layer is formed by means of the application or accumulation of a material to a substrate or another layer using processes associated with thick film, thin film, thermal atomization or sol -gel, among others. These processes are also determined as "stratified processes", "stratification processes" or "stratified heater processes".

Referring now to Figure 3a, an additional functional layer between the substrate 12 and the dielectric layer 14 may be beneficial or even required when thermal atomization processes are used for the dielectric layer 14. This layer is referred to as a link layer 30 and it functions to promote the adhesion of the thermally atomized dielectric layer 14 to the substrate 12. The bonding layer 30 is preferably formed on the substrate 12 using a layered process such as wire arc atomization and is preferably a material such as a nickel alloy -aluminum. As shown in Figure 3b, yet another functional layer can be used between the substrate 12 and the dielectric layer 14. This layer is referred to as a graduated layer 32 and is used to provide a CTE transition between the substrate 12 and the dielectric layer 14. when the difference CTE between these layers is relatively large. For example, when the substrate 12 is metal and the dielectric layer 14 is ceramic, the difference CTE is relatively large and the structural integrity of the stratified heater 10 would be degraded due to this difference. Thus, the graduated layer 32 provides a CTE transition as illustrated in Figure 4, which may be linear / continuous or gradually changed as shown by the continuous and discontinuous lines, respectively or another function as required by specific application requirements. The material for the graduated layer 32 is preferably a cermet, a material consisting of a combination of ceramic and metal powders, however, other materials may also be used as long as they remain within the scope of the present invention. Referring now to Figure 3c, both a link layer 30 and a step layer 32 as previously described can be used in another form of the present invention. As shown, the link layer 30 is formed on the substrate 12 and the graduated layer 32 is formed on the link layer 30, while the link layer 30 is used to promote an improved adhesion characteristic between the substrate 12 and the graduated layer 32. Similarly, the dielectric layer 14 is formed on the graduated layer 32 and thus the graduated layer 32 provides a CTE transition from the substrate 12 to the dielectric layer 14. As shown in Figure 5, the laminated heater 10 can also using an additional functional layer that is formed on the protective layer 18, i.e. a coating layer 40. The coating layer 40 is preferably formed using a layered process and may include by way of example a machinable metal layer, a layer of non-stick coating, an emissivity modifier layer, a thermal insulating layer, a visible performance layer (for example, temperature sensitive material indi the temperature via color) or a layer that improves durability, among others. There may also be additional preparation layers between the protective layer 18 and the coating layer 40 in order to improve the performance of the coating layer 40 as long as it remains within the scope of the present invention. Thus, functional layers as shown and described herein should not be construed as limiting the scope of the present invention. Additional functional layers, in addition, in different places throughout the combination of layers, can be used according to specific application requirements. These functional layers may also include additional resistive layers as shown in Figure 6, where a plurality of resistive layers 42 are formed over a corresponding plurality of dielectric layers 44. The plurality of resistive layers 42 may be required for a heater outlet. additional in the form of power and may also be used for redundancy of the stratified heater 10, for example in the event that the resistive layer 16 fails. In addition, the plurality of resistive layers 42 can also be used to meet resistance requirements for applications where high or low resistance is required in a small effective heated area or on a limited footprint. Additionally, multiple circuits or resistive layer patterns may be used within the same resistive layer or between several layers, so long as it remains within the scope of the present invention. For example, each of the resistive layers 42 may have different patterns or may be electrically joined to alternative powder terminals. Thus, the configuration of the plurality of resistive layers 42 as illustrated should not be construed as limiting the scope of the present invention. Additional forms of functional layers are illustrated in Figures 7a-7d, which are intended to be exemplary and not to limit the possible functional layers for the laminated heater 10 in accordance with the teachings of the present invention. As shown in Figure 7a, the additional functional layer is a detector layer 50. The detector layer 50 is preferably a resistance temperature detector (RTD) temperature sensor and is formed on a dielectric layer 52 using a film process. thin, although other processes may be used in accordance with the teachings of the present invention. Figure 7b illustrates a stratified heater 10 having a functional layer of a grounding shield 60, which is used to isolate and drain any current leakage to or from the stratified heater 10. As shown, the grounding shield 60 is formed between dielectric layers 14 and 62 and is connected to a separate terminal for proper connection to a path Designated leakage 64. The grounding shield 60 is preferably formed using a thick film laminated process, however, other layered processes as referred to herein may also be used as long as they remain within the scope of the present invention. . As shown in Figure 7c, the additional functional layer is an electrostatic shield 70, which is used to dissipate the electrostatic energy directed to / or from the stratified heater 10. Preferably, the electrostatic shield 70 is formed between a dielectric layer 72 and a protective layer 74 as shown. Figure 6d illustrates the additional functional layer of a radio frequency (RF) shield 80, which is used to shield certain frequencies to / from the stratified heater 10. Similarly, the RF shield 80 is formed between a dielectric layer 82 and a layer protective 84 as shown. The electrostatic shielding 70 and RF shielding 80 layers are preferably formed using a thick film lamination process, however other laminating processes may also be used as long as they remain within the scope of the present invention. It should be understood that the additional functional layers as shown and described herein, ie the detector layer 50, the grounding shield 60, the electrostatic shield 70 and the RF shield 80 can be placed at several sites adjacent to any of the layers of the stratified heater 10 and connected to an appropriate energy source different from those positions and connections illustrated in FIGS. Id as long as they remain within the scope of the present invention. In addition to using functional layers as described herein, the layered processes can also be used to embed or embed discrete components within the layered heater 10. For example, as shown in FIG. 8, a discrete component 90 (e.g. , temperature detector) is embedded between the dielectric layer 14 and the protective layer 18. The discrete component 90 is preferably secured to the resistive layer 16 using the thermal atomization process, which would result in a local securing layer 92 as shown in FIG. sample. However, other processes may be used to secure discrete embedded components as long as they remain within the scope of the present invention. Additional discrete components may include, but are not limited to, thermocouples, RTDs, thermistors, voltage meters, thermal fuses, optical fibers and microprocessors and controllers, among others. It should be understood that the position within the additional functional layers and the discrete components is not intended to limit the scope of the present invention. Additional functional layers and discrete components can be placed at several sites adjacent to any one of the layers, for example between the dielectric layer 14 and the resistive layer 14, between the resistive layer 14 and the protective layer 16, between the substrate 12 and the dielectric layer 14 or adjacent to other layers, so long as it remains within the scope of the present invention. The description of the invention is only exemplary in nature and thus, variations that do not deviate from the scope of the invention are intended to be within the scope of the invention. For example, the stratified heater 10 as described herein may be used with a two-wire controller as shown and described in co-pending US Patent Application Serial No. 10 / 719,327, entitled "T o-Wire Layered. Heater System "filed on November 21, 2003 and the co-pending US patent application" Tailored Heat Transfer Layered Heater System "filed on January 6, 2004, both of which are assigned in common with the present application and the content of which is incorporated herein by reference in its entirety. Such variations will not be considered as a deviation from the spirit and scope of the invention.

Claims (22)

1. CLAIMS 1. A stratified heater characterized in that it comprises: a plurality of resistive layers separated by a corresponding plurality of dielectric layers, wherein the plurality of resistive layers are formed on the corresponding plurality of dielectric layers and the plurality of resistive layers and dielectric layers are formed by at least one stratified process. The stratified heater according to claim 1, characterized in that the laminating process is selected from the group consisting of coarse film, thin film, thermal atomization and sol -gel. 3. The stratified heater according to claim 1, characterized in that it further comprises a substrate, wherein one of the plurality of dielectric layer is formed on the substrate. The stratified heater according to claim 3, characterized in that the substrate is selected from the group consisting of copper coated with nickel, aluminum, stainless steel, low carbon steel, tool steel, refractory alloy, aluminum oxide and aluminum nitride. The stratified heater according to claim 1, characterized in that it also comprises at least one conductor block in contact with at least one of the resistive layers. The stratified heater according to claim 5, characterized in that the conductor block is formed by a layered process selected from the group consisting of thick film, thin film, thermal atomization and sol-gel. The stratified heater according to claim 1, characterized in that it further comprises: a two-wire controller in communication with the stratified heater, wherein at least one of the resistive layers has characteristics of sufficient temperature resistance coefficient of such Thus, the resistive layer is a heater element and a temperature sensor and the two-wire controller determines the temperature of the stratified heater using the resistance of the resistive layer and controls the heater temperature accordingly. 8. A stratified heater characterized in that it comprises: a dielectric layer; a resistive layer formed on the dielectric layer; a protective layer formed on the resistive layer and at least one functional layer formed within the laminated heater adjacent to at least one of the layers, wherein each of the layers is formed by at least one layered process. The stratified heater according to claim 8, characterized in that the functional layer is selected from the group consisting of a protective layer, a grounding layer, an electrostatic layer and an RF layer. The stratified heater according to claim 8, characterized in that the laminating process is selected from the group consisting of thick film, thin film, thermal atomization and sol-gel. The stratified heater according to claim 8, characterized in that it further comprises at least one discrete component embedded within the laminated heater. The stratified heater according to claim 11, characterized in that the discrete component is selected from the group consisting of a thermocouple, a CRT, a thermistor, a voltage meter, a thermal fuse, an optical fiber, a microprocessor and a controller. 13. A stratified heater characterized in that it comprises: a dielectric layer formed by a thermal atomization process and a resistive layer disposed on the dielectric layer, the resistive layer is formed by a thin film process. 14. A stratified heater characterized in that it comprises: a substrate; a bond layer formed on the substrate; a dielectric layer formed on the bonding layer, the dielectric layer is formed by a first layered process and a resistive layer formed on the dielectric layer, the resistive layer is formed by a second layered process, wherein the first layered process is different than the second stratified process. 15. The stratified heater according to claim 14, characterized in that it further comprises: a protective layer formed on the resistive layer, the protective layer is formed by a layered process. 16. A stratified heater characterized in that it comprises: a substrate; a graduated layer formed on the substrate; a dielectric layer formed on the link layer, the dielectric layer is formed by a first stratified process and a resistive layer formed on the dielectric layer, the resistive layer is formed by a second stratified process, wherein the first stratified process is different than the second stratified process. 17. The stratified heater according to claim 16, characterized in that it further comprises: a protective layer formed on the resistive layer, the protective layer is formed by a stratified process. 18. A stratified heater characterized in that it comprises: a dielectric layer formed by a first stratified process; a resistive layer formed on the dielectric layer, the resistive layer is formed by a second stratified process; a protective layer formed on the resistive layer, the protective layer is formed by a layered process and a coating layer formed on the protective layer, the coating layer is formed by a layered process, wherein the first layered process is different than the layered process. second stratified process. The stratified heater according to claim 18, characterized in that the coating layer is selected from the group consisting of a machinable metal layer, a non-adherent coating layer, an emissivity modifier layer, a thermal insulating layer and a layer that improves durability. 20. A stratified heater characterized in that it comprises: a dielectric layer formed by a sol-gel process; a resistive layer formed on the dielectric layer, the resistive layer is formed by a thick film process and a protective layer formed on the resistive layer, the protective layer is formed by a sol-gel process. 21. A stratified heater characterized in that it comprises: a dielectric layer formed by a thermal atomization process; a resistive layer formed on the dielectric layer, the resistive layer is formed by a thick film process and a protective layer formed on the resistive layer, the protective layer is formed by a sol-gel process. 22. A stratified heater characterized in that it comprises: a dielectric layer formed by a sol-gel process; a resistive layer formed on the dielectric layer, the resistive layer is formed by a thermal atomization process and a protective layer formed on the resistive layer, the protective layer is formed by a sol-gel process.