Ceramic heat-sensitive device

Abstract

A ceramic heat-sensitive device includes a ceramic body, an inner electrode layer, and an outer electrode layer. The ceramic body exhibits a positive temperature coefficient (PTC) characteristic and includes a top surface, a bottom surface, a first end surface, and a second end surface. The top surface is disposed opposite to the bottom surface, and the first end surface is disposed opposite to the second end surface. The first end surface and the second end surface are connected to the top surface and the bottom surface. The inner electrode layer is positioned on two terminals of the top surface, with a gap separating them. The outer electrode layer covers the inner electrode layer.

Description

Technical Field

[0001] This invention relates to a ceramic thermistor, and more specifically, to a ceramic thermistor with low resistance and good resistance rise performance. Prior Technology

[0002] The resistance of a conventional positive temperature coefficient (PTC) element is highly sensitive to temperature changes. Under normal operating conditions, the resistance of a PTC element remains extremely low, allowing the circuit to function properly. However, when overcurrent or overheating occurs, causing the temperature to rise to a critical temperature, also known as the Curie point, the resistance will instantly jump to a high resistance state (e.g., above 10⁴ Ω), a phenomenon known as a "trip," thus cutting off the excessive current and protecting the battery or circuit components. Therefore, PTC elements are now integrated into various circuit components to prevent damage from overcurrent.

[0003] Positive temperature coefficient (PTC) elements can be broadly classified into two categories: polymer PTC elements and ceramic PTC elements. Commonly known PPTC elements exhibit poor resistance hysteresis after tripping, meaning their resistance hysteresis is poor, and they are not resistant to high voltages. While CPTC elements generally withstand high voltages and their resistance can recover to a value closer to their original value, their relatively high normal resistance results in poor conductivity, thus limiting their application range.

[0004] Furthermore, due to the material differences in the positive temperature coefficient (PTC) layers of the two devices, the structural design of the internal electrodes also differs. The PTC layer of a PPTC device is primarily composed of polymer and conductive fillers. After mixing, the conductive polymer is pressed into a thin sheet, and then copper foil is placed on top and below the sheet for hot-pressing to form a three-layer structure. The copper foil can then be etched with different patterns to form the internal electrodes of the PPTC device. The PTC layer of a CPTC device is primarily composed of ceramic materials. The ceramic material must first undergo a sintering process to form a conductive ceramic substrate, and then metal materials are printed and sintered to form the internal electrodes. It should be understood that compared to the internal electrodes of PPTC devices, the design freedom of the internal electrodes of CPTC devices is lower, and standardized designs are already widely available in the industry. Please refer to Figures 1a and 1b.

[0005] Figure 1a shows a perspective view of a conventional CPTC element, while Figure 1b shows a cross-sectional view of the CPTC element of Figure 1a along line segment AA. The conventional CPTC element comprises a ceramic body 1 (i.e., the aforementioned conductive ceramic substrate), an inner electrode layer 2, and an outer electrode layer 3. The inner electrode layer 2 is formed on both end faces of the ceramic body 1, while the outer electrode layer 3 covers the inner electrode layer 2 and further covers all exposed areas at both ends of the ceramic body 1. It can be noted that placing the inner electrode layer 2 at both ends results in excessively large distances between them, causing excessively high resistance when the element is not activated (i.e., not triggered). If the ceramic body 1 is shortened to reduce resistance, there are dimensional limitations; besides failing to achieve satisfactory low resistance performance, it is more likely to cause unintended changes in other electrical characteristics.

[0006] In view of this, there is an urgent need to develop a low-resistance ceramic thermistor that also performs well in other electrical characteristics. Summary of the Invention

[0007] According to one embodiment of the present invention, a ceramic thermistor includes a ceramic body, an inner electrode layer, and an outer electrode layer. The ceramic body has a positive temperature coefficient and includes a top surface, a bottom surface, a first end surface, and a second end surface. The top surface and the bottom surface are disposed opposite each other, while the first end surface and the second end surface are disposed opposite each other and connected to the top surface and the bottom surface. The inner electrode layer is disposed at both ends of the top surface, and the inner electrode layers at both ends are separated by a gap. The outer electrode layer covers the inner electrode layer.

[0008] According to some embodiments, the ceramic body further includes a first side surface and a second side surface opposite to the first side surface, connecting the top surface, bottom surface, first end surface, and second end surface, thereby forming a hexahedron. The outer electrode layer extends and covers the first end surface and the second end surface, but does not cover the first side surface and the second side surface.

[0009] According to some embodiments, the ceramic thermistor further includes an insulating layer covering the top surface of the ceramic body. The insulating layer is disposed within the spacing of the inner electrode layers at both ends.

[0010] According to some embodiments, the inner electrode layer has an inner electrode top surface and a first sidewall. The inner electrode top surface is parallel to the top surface of the ceramic body, while the first sidewall extends perpendicularly from the inner electrode top surface to the top surface. An insulating layer extends to the first sidewall, thereby partially covering the insulating layer and the first sidewall with respect to the outer electrode layer.

[0011] According to some embodiments, the insulating layer completely covers the first sidewall of the inner electrode layer and extends further to the top surface of the inner electrode, thereby partially covering the insulating layer and the top surface of the inner electrode with the outer electrode layer.

[0012] According to some embodiments, the inner electrode layer has an inner electrode top surface and a first sidewall. The inner electrode top surface is parallel to the top surface of the ceramic body, while the first sidewall extends perpendicularly from the inner electrode top surface to the top surface. An outer electrode layer covers the first sidewall and the inner electrode top surface of the inner electrode layer. An insulating layer extends to the outer electrode layer and further extends parallel to the first sidewall and covers the outer electrode layer.

[0013] According to some embodiments, the insulating layer further covers the bottom surface, the first side surface, and the second side surface of the ceramic body, so that only the insulating layer and the outer electrode layer of the ceramic thermistor are exposed to the external environment.

[0014] According to some embodiments, the spacing is 0.4 mm to 0.45 mm.

[0015] According to some embodiments, the inner electrode layer has a width extending toward the first end face and the second end face, and the width is 0.15 mm to 0.21 mm.

[0016] According to some embodiments, the material of the inner electrode layer does not contain titanium.

[0017] According to some embodiments, the material of the inner electrode layer is selected from the group consisting of nickel, chromium, nickel-chromium alloys, nickel-copper alloys, silver, aluminum, and combinations thereof.

[0018] According to some embodiments, the ceramic body comprises a first component and a second component. The first component comprises barium, strontium, calcium, and a first trace element. The second component comprises titanium, manganese, and a second trace element. The first and second trace elements are selected from the group consisting of ytterbium, lanthanum, cerium, antimony, tungsten, neodymium, samarium, europium, thorium, tantalum, erbium, thionium, and combinations thereof. The volume resistivity of the ceramic body is less than 10 Ω·cm.

[0019] According to some embodiments, with the total mole number of barium, strontium, calcium and the first trace element being 100%, and strontium accounting for 20% to 25%; calcium accounting for 4.5% to 5%; and the first trace element accounting for 0.13% to 0.17%, the Curie temperature of the ceramic body is 85°C to 91°C.

[0020] According to some embodiments, the total mole count of titanium, manganese and the second trace element is 100%, with manganese accounting for 0.01% to 0.03% and the second trace element accounting for 0.02% to 0.04%.

[0021] According to some embodiments, the ceramic body has a first resistance value at 25°C and a second resistance value at 125°C. The ratio of the second resistance value to the first resistance value is 10 or more.

[0022] According to one embodiment of the present invention, a ceramic thermistor includes a ceramic body, an inner electrode layer, and an outer electrode layer. The ceramic body has a positive temperature coefficient and includes a top surface, a bottom surface, a first end surface, and a second end surface. The top surface and the bottom surface are disposed opposite each other, while the first end surface and the second end surface are disposed opposite each other and connected to the top surface and the bottom surface. The inner electrode layer is disposed at both ends of the top surface, and the inner electrode layers at both ends are separated by a gap. The outer electrode layer covers the inner electrode layer and the top surface of the ceramic body, and does not extend to the first end surface and the second end surface.

[0023] According to some embodiments, the ceramic body further includes a first side surface and a second side surface opposite to the first side surface, connecting the top surface, bottom surface, first end surface, and second end surface, thereby forming a hexahedron. The outer electrode layer does not cover the first side surface and the second side surface.

[0024] According to some embodiments, an insulating layer covers the top surface of the ceramic body. The insulating layer is disposed within the spacing of the inner electrode layers at both ends.

[0025] According to some embodiments, the inner electrode layer has an inner electrode top surface and a first sidewall. The inner electrode top surface is parallel to the top surface of the ceramic body, while the first sidewall extends perpendicularly from the inner electrode top surface to the top surface. An insulating layer extends to the first sidewall, thereby partially covering the insulating layer and the first sidewall with respect to the outer electrode layer.

[0026] According to some embodiments, the insulating layer completely covers the first sidewall of the inner electrode layer and extends further to the top surface of the inner electrode, thereby partially covering the insulating layer and the top surface of the inner electrode with the outer electrode layer.

[0027] According to some embodiments, the inner electrode layer has an inner electrode top surface and a first sidewall. The inner electrode top surface is parallel to the top surface of the ceramic body, while the first sidewall extends perpendicularly from the inner electrode top surface to the top surface. An outer electrode layer covers the first sidewall and the inner electrode top surface of the inner electrode layer. An insulating layer extends to the outer electrode layer and further extends parallel to the first sidewall and covers the outer electrode layer.

[0028] According to some embodiments, the insulating layer further covers the bottom surface, first side surface, second side surface, first end surface, and second end surface of the ceramic body.

[0029] According to some embodiments, the spacing is 0.4 mm to 0.45 mm.

[0030] According to some embodiments, the inner electrode layer has a width extending toward the first end face and the second end face, and the width is 0.15 mm to 0.21 mm.

[0031] According to some embodiments, the material of the inner electrode layer does not contain titanium.

[0032] According to some embodiments, the material of the inner electrode layer is selected from the group consisting of nickel, chromium, nickel-chromium alloys, nickel-copper alloys, silver, aluminum, and combinations thereof.

[0033] According to some embodiments, the ceramic body comprises a first component and a second component. The first component comprises barium, strontium, calcium, and a first trace element. The second component comprises titanium, manganese, and a second trace element. The first and second trace elements are selected from the group consisting of ytterbium, lanthanum, cerium, antimony, tungsten, neodymium, samarium, europium, thorium, tantalum, erbium, thionium, and combinations thereof. The volume resistivity of the ceramic body is less than 10 Ω·cm.

[0034] According to some embodiments, with the total mole number of barium, strontium, calcium and the first trace element being 100%, and strontium accounting for 20% to 25%; calcium accounting for 4.5% to 5%; and the first trace element accounting for 0.13% to 0.17%, the Curie temperature of the ceramic body is 85°C to 91°C.

[0035] According to some embodiments, the total mole count of titanium, manganese and the second trace element is 100%, with manganese accounting for 0.01% to 0.03% and the second trace element accounting for 0.02% to 0.04%.

[0036] According to some embodiments, the ceramic body has a first resistance value at 25°C and a second resistance value at 125°C. The ratio of the second resistance value to the first resistance value is 10 or more. Simple Explanation of the Diagram

[0037] Figures 1a and 1b show a perspective view and a cross-sectional view of a conventional ceramic positive temperature coefficient element, respectively; Figure 2 shows a perspective view of a first embodiment of the ceramic thermistor of the present invention; Figures 3a, 3b, and 3c show the cross-sectional view, top view, and front view of the ceramic thermistor in Figure 2, respectively; Figure 3d shows a magnified view of the area within the dashed box in Figure 3a; Figure 4 shows a perspective view of a second embodiment of the ceramic thermistor of the present invention; Figures 5a, 5b, and 5c show the cross-sectional view, top view, and front view of the ceramic thermistor in Figure 4, respectively; Figure 5d shows a magnified view of the area within the dashed box in Figure 5a; Figures 6a to 7b show cross-sectional views of various embodiments of the present invention; and Figure 8 shows the temperature curves during the sintering process. Implementation

[0038] To make the above and other technical contents, features and advantages of the present invention more apparent and understandable, relevant embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings.

[0039] Please refer to Figures 2 to 3d, which show various views of a first embodiment of the ceramic thermistor 100 of the present invention. The ceramic thermistor 100 of the present invention includes a ceramic body 10, an inner electrode layer 20, an outer electrode layer 30, and an insulating layer 40. The ceramic body 10 is a hexahedron with a positive temperature coefficient (i.e., a hexahedron including a top surface 11, a bottom surface 12, a first end surface 13, a second end surface 14, a first side surface 15, and a second side surface 16). In Figure 2, the outer electrode layer 30 is located at both ends of the ceramic body 10 and extends from the top surface 11 and the bottom surface 12, covering the entire end surface (i.e., the first end surface 13 and the second end surface 14) but not covering the first side surface 15 and the second side surface 16. The remaining portion of the ceramic body 10 exposed to the external environment is covered by the insulating layer 40. Thus, a ceramic thermistor 100 is formed where three sides at each end are covered by the outer electrode layer 30.

[0040] Please refer to Figure 3a, which is a cross-sectional view of the ceramic thermistor 100 in Figure 2 along line AA. To enable electrical conduction between the ceramic body 10 and an external power source, an inner electrode layer 20 with good ohmic contact must first be formed on it; therefore, the inner electrode layer 20 can also be called an ohmic contact electrode. The material of the inner electrode layer 20 can be selected from the group consisting of nickel (Ni), chromium (Cr), nickel-chromium alloy (Ni-Cr alloy), nickel-copper alloy (Ni-Cu alloy), silver (Ag), aluminum (Al), and combinations thereof, and can be formed by printing, coating, vapor deposition, or other conventional film-forming methods. For example, a nickel-chromium alloy can be formed into a paste and printed on the surface, and then sintered to form the inner electrode layer 20. Furthermore, considering the applicability of the material, the material of the inner electrode layer 20 of the present invention does not include titanium. It should also be noted that, to shorten the current conduction distance, the inner electrode layer 20 of the present invention is not disposed on the first end face 13 and the second end face 14. More specifically, the inner electrode layer 20 is disposed at both ends of the top surface 11 and the bottom surface 12, and the inner electrode layers 20 at both ends are separated by a distance G. That is, the inner electrode layer 20 on the top surface 11 is divided into two independent blocks located at its two ends, separated from each other by at least a distance G; while the inner electrode layer 20 on the bottom surface 12 is divided into two independent blocks located at its two ends, separated from each other by at least a distance G. In other words, taking the left side of the cross-sectional view as an example, the inner electrode layer 20 extends to the right along the z-axis from the junction of the first end face 13 with the top surface 11 and the bottom surface 12; and taking the right side of the cross-sectional view as an example, the inner electrode layer 20 extends to the left along the z-axis from the junction of the second end face 14 with the top surface 11 and the bottom surface 12. Accordingly, the inner electrode layer 20 is only disposed on the top surface 11 and the bottom surface 12, and does not cover the first end face 13, the second end face 14, the first side face 15, and the second side face 16. It should be understood that the inner electrode layer 20 can be a single layer or multiple layers. In one embodiment, the inner electrode layer 20 is a multilayer structure, that is, multiple layers are stacked along the y-axis direction, wherein the materials of each layer may be the same or different.

[0041] To improve the weather resistance and insulation of the non-electrical connection areas of the ceramic body 10, the present invention further provides an insulating layer 40 within the spacing G of the inner electrode layer 20. The insulating material can be printed on the areas without the inner electrode layer 20, and then sintered to form the insulating layer 40. In addition to the areas covered by the inner electrode layer 20, the insulating layer 40 covers the remaining areas of the top surface 11 and the bottom surface 12, and further covers the first side surface 15 and the second side surface 16 (see Figure 2). Furthermore, as mentioned above, the present invention may include an outer electrode layer 30. The outer electrode layer 30 covers a portion of the insulating layer 40 and encapsulates the entire inner electrode layer 20. The outer electrode layer 30 can be formed by electroplating or chemical plating. For example, nickel (Ni) or tin (Sn) is plated onto the inner electrode layer 20, and the aforementioned nickel or tin layer is the outer electrode layer 30. Of course, the outer electrode layer 30 can be a single layer or multiple layers. In one embodiment, the outer electrode layer 30 is a multilayer structure, wherein the materials of each layer can be the same or different.

[0042] To more clearly explain the configuration relationship of the inner electrode layer 20, the outer electrode layer 30, and the insulating layer 40, please refer to Figure 3d. Figure 3d shows a partial enlarged view of the ceramic thermistor 100 in Figure 3a within the dashed box. The inner electrode layer 20 has an inner electrode top surface 21, an inner electrode bottom surface 22, a first sidewall 23, and a second sidewall 24. The inner electrode top surface 21 is parallel to the top surface 11 of the ceramic body 10 and is disposed opposite to the inner electrode bottom surface 22. The first sidewall 23 and the second sidewall 24 are disposed opposite to each other and connect the inner electrode top surface 21 and the inner electrode bottom surface 22. That is, the first sidewall 23 extends vertically from the inner electrode top surface 21 to the top surface 11, and the second sidewall 24 also extends vertically from the inner electrode top surface 21 to the top surface 11. The bottom surface 22 of the inner electrode is substantially coplanar with the top surface 11 of the ceramic body 10, while the second sidewall 24 is substantially coplanar with the second end face 14, so that the second sidewall 24 of the inner electrode layer 20 and the second end face 14 of the ceramic body 10 are flush when viewed along the y-axis. Of course, in some embodiments, the second sidewall 24 may also be designed not to be coplanar with the second end face 14 (not shown), so that the second sidewall 24 of the inner electrode layer 20 and the second end face 14 of the ceramic body 10 are stepped when viewed along the y-axis. To avoid the influence of plating, moisture or other external factors, the insulating layer 40 is designed to fit as closely as possible to the interface between the electrode and the ceramic body 10. The insulating layer 40 covers the top surface 11 of the ceramic body 10 and extends along the x-axis to the first sidewall 23 of the inner electrode layer 20. The outer electrode layer 30 partially covers the insulating layer 40 and the first sidewall 23 of the inner electrode layer 20, and continues to extend to the top surface 21 of the inner electrode, the second sidewall 24 and the second end face 14 of the ceramic body 10. Furthermore, as mentioned above, the outer electrode layer 30 covers the entire inner electrode layer 20, meaning that the outer electrode layer 30 also covers the inner electrode layer 20 in the yz plane (as shown in Figure 2). Thus, only the insulating layer 40 and the outer electrode layer 30 of the ceramic thermistor 100 are exposed to the external environment. It should be understood that the same configuration as described above can also be present on the bottom surface 12 of the ceramic body 10.

[0043] Please refer to Figures 4 to 5d for various views showing a second embodiment of the ceramic thermistor 200 of the present invention. The main difference between the ceramic thermistor 200 and the ceramic thermistor 100 lies in the area covered by the outer electrode layer 30. In the ceramic thermistor 200, the outer electrode layer 30 does not cover the second sidewall 24 of the inner electrode layer 20, nor does it cover the first end face 13 and the second end face 14. More specifically, the ceramic thermistor 200 includes a ceramic body 10, an inner electrode layer 20, an outer electrode layer 30, and an insulating layer 40. The ceramic body 10 is a hexahedron with a positive temperature coefficient (i.e., a hexahedron including a top surface 11, a bottom surface 12, a first end face 13, a second end face 14, a first side face 15, and a second side face 16). In Figure 4, the outer electrode layer 30, located at both ends of the top surface 11 and the bottom surface 12 of the ceramic body 10, does not cover the first side surface 15 and the second side surface 16, nor does it extend towards the second sidewall 24 of the inner electrode layer 20, thus not covering the first end surface 13 and the second end surface 14. Similarly, the remaining portions of the ceramic body 10 exposed to the external environment are covered by the insulating layer 40. Thus, a ceramic thermistor 200 is formed, with two sides covered by the outer electrode layer 30 at each end.

[0044] Please refer to Figures 5a and 5d. Figure 5a is a cross-sectional view of the ceramic thermistor 200 in Figure 4 along line AA. Figure 5d shows a partial enlarged view of the ceramic thermistor 200 in Figure 5a within the dashed box. The inner electrode layer 20 has an inner electrode top surface 21, an inner electrode bottom surface 22, a first sidewall 23, and a second sidewall 24. The inner electrode top surface 21 is parallel to the top surface 11 of the ceramic body 10 and is disposed opposite to the inner electrode bottom surface 22. The first sidewall 23 and the second sidewall 24 are disposed opposite to each other and connect the inner electrode top surface 21 and the inner electrode bottom surface 22. The inner electrode bottom surface 22 is substantially coplanar with the top surface 11 of the ceramic body 10. That is, the first sidewall 23 extends vertically from the inner electrode top surface 21 to the top surface 11, and the second sidewall 24 also extends vertically from the inner electrode top surface 21 to the top surface 11. It should also be noted that the second sidewall 24 is coplanar with the second end face 14, resulting in a flush design between the second sidewall 24 of the inner electrode layer 20 and the second end face 14 of the ceramic body 10 when viewed along the y-axis, thus exposing the second sidewall 24 to the external environment. Of course, in some embodiments, the second sidewall 24 may also be designed to be non-coplanar with the second end face 14 (not shown), resulting in a stepped design between the second sidewall 24 of the inner electrode layer 20 and the second end face 14 of the ceramic body 10 when viewed along the y-axis; in this way, the outer electrode layer 30 can completely cover the second sidewall 24 during the manufacturing process. Similarly, to avoid the influence of plating penetration, moisture, or other external factors, the insulating layer 40 will be as close as possible to the interface between the electrode and the ceramic body 10. The insulating layer 40 covers the top surface 11 of the ceramic body 10 and extends along the x-axis to the first sidewall 23 of the inner electrode layer 20. The outer electrode layer 30 partially covers the insulating layer 40 and the first sidewall 23 of the inner electrode layer 20, and continues to the top surface 21 of the inner electrode, ending at the junction of the top surface 21 of the inner electrode and the second sidewall 24. Thus, the outer electrode layer 30 does not extend to the second end face 14. Furthermore, the outer electrode layer 30 also covers the inner electrode layer 20 in the yz plane (as shown in Figure 4). Thus, only the second sidewall 24 of the inner electrode layer 20, the insulating layer 40, and the outer electrode layer 30 are exposed to the external environment in the ceramic thermistor element 200. It is also understood that components identical to those described above use the same component symbols and can have the same functions and configurations as described above. To avoid redundancy, the remaining components will not be described again here.

[0045] The configuration relationship between the layers can also be adjusted as needed, as shown in the various embodiments in Figures 6a to 7b.

[0046] Figures 6a and 6b show cross-sectional views of embodiments of the ceramic thermistor 100 and ceramic thermistor 200, respectively. Compared to Figure 3a, the insulating layer 40 in Figure 6a covers the inner wall of the outer electrode layer 30. Similarly, compared to Figure 5a, the insulating layer 40 in Figure 6b covers the inner wall of the outer electrode layer 30. Specifically, the outer electrode layer 30 covers the top surface 21 of the inner electrode of the inner electrode layer 20, continues to completely cover the first sidewall 23 of the inner electrode layer 20 along the y-axis, and connects to the top surface 11 of the ceramic body 10. The insulating layer 40 extends along the z-axis on the top surface 11 to the outer electrode layer 30, and further extends parallel to the first sidewall 23 of the inner electrode layer 20 along the y-axis and covers the outer electrode layer 30. Thus, the insulating layer 40 is formed on the inner walls of opposite sides of the outer electrode layer 30, which can effectively prevent the generation of electric arc between the two electrodes. It should also be understood that components identical to those described above use the same component symbols and can have the same functions and configurations as described above. To avoid redundancy, the remaining components will not be described again here.

[0047] Figures 7a and 7b show cross-sectional views of embodiments of ceramic thermistor 100 and ceramic thermistor 200, respectively. Compared to Figure 3a, the insulating layer 40 in Figure 7a further covers the inner wall and part of the top surface of the inner electrode layer 20. Similarly, compared to Figure 5a, the insulating layer 40 in Figure 7b further covers the inner wall and part of the top surface of the inner electrode layer 20. Specifically, the insulating layer 40 extends along the z-axis on the top surface 11 to the first sidewall 23 of the inner electrode layer 20, continues to extend along the y-axis and completely covers the first sidewall 23, and finally extends along the z-axis to the top surface 21 of the inner electrode. Thus, the outer electrode layer 30 and the first sidewall 23 of the inner electrode layer 20 are not in direct contact, while the insulating layer 40 is located between them. The insulating layer 40 penetrates deeper into the interface between the inner and outer electrodes, providing more comprehensive protection. It is also understood that the same components as those described above use the same component symbols and can have the same functions and configurations as described above. To avoid redundancy, the remaining components will not be described again here.

[0048] Furthermore, the present invention further improves the material composition of the ceramic body 10 in conjunction with the aforementioned structural design.

[0049] Table 1 Group Composition percentage (mol%) Electrical characteristics The first component (Ba + Sr + Ca + R1 = 100%) The second component (Ti + Mn + R2 = 100%) Sr Ca R1 Mn R2 ρ (Ω.cm) Tc (℃) R125 / R25 C1 15 3.0 0.13 0.01 0.02 12.63 103 42.5 E1 20 4.5 0.13 0.01 0.02 8.16 91 45.3 E2 23 4.5 0.13 0.01 0.02 8.43 88 46.5 E3 25 4.5 0.13 0.01 0.02 8.38 86 45.8 E4 20 4.8 0.13 0.01 0.02 8.62 89 42.4 E5 20 5.0 0.13 0.01 0.02 7.98 91 43.4 E6 25 5.0 0.13 0.01 0.02 9.03 85 46.5 E7 20 4.5 0.15 0.01 0.02 6.49 89 39.8 E8 20 4.5 0.17 0.01 0.02 9.65 90 46.1 E9 25 5.0 0.17 0.01 0.02 9.88 86 42.5 C2 30 4.5 0.17 0.01 0.02 8.65 72 44.6 C3 25 5.0 0.20 0.01 0.02 18.31 88 49.8 E10 20 4.5 0.15 0.02 0.02 7.89 88 56.5 E11 20 4.5 0.15 0.03 0.02 10.01 86 86.8 C4 20 4.5 0.15 0.04 0.02 23.8 84 103.8 C5 20 4.5 0.15 0.02 0.01 13.64 91 62.3 E12 20 4.5 0.15 0.02 0.03 7.28 90 53.2 E13 20 4.5 0.15 0.01 0.04 9.24 89 41.6 C6 20 4.5 0.15 0.01 0.05 16.85 88 47.2

[0050] R1 refers to the first trace element. R2 refers to the second trace element. ρ refers to volume resistivity. Tc refers to the Curie point, defined as the temperature at which the resistance at 25°C is twice that at 25°C. To meet industry requirements, the Curie point (Tc) is ideally controlled within the range of approximately 85°C to approximately 90°C. R125 / R25 refers to the rate of change of resistance, defined as the ratio of the resistance of the ceramic body 10 at 125°C to its resistance at 25°C. That is, the ceramic body has a first resistance value at 25°C and a second resistance value at 125°C. The ratio of the second resistance value to the first resistance value is R125 / R25.

[0051] The preparation method of ceramic body 10 is described below.

[0052] First, barium carbonate (BaCO₃), strontium carbonate (SrCO₃), calcium carbonate (CaCO₃), titanium dioxide (TiO₂), manganese dioxide (MnO₂), and trivalent and pentavalent semiconductor elements are mixed with a dispersant and water, and then mixed using a ball mill to form a slurry. The aforementioned trivalent and pentavalent semiconductor elements are selected from the group consisting of ytterbium (Y), lanthanum (La), cerium (Ce), antimony (Sb), plutonium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), thiocyanate (Gd), tantalum (Ta), erbium (Er), thionium (Tm), and combinations thereof. After filtration and drying, the slurry is calcined at a temperature of 800°C to 1000°C to form ceramic powder. The ceramic powder is mixed with a binder and then granulated to form numerous ceramic particles. These ceramic particles were then hot-pressed into plate-shaped ceramic blanks, which were subsequently placed in a sintering furnace and sintered under atmospheric conditions to form ceramic body 10. The sintering temperature was 1320℃, and the temperature was held for one hour. The oxygen content in the sintering atmosphere in the sintering furnace was 21%. Ceramic body 10 was then subjected to elemental analysis and electrical property testing, and the results are shown in Table 1.

[0053] As shown in Table 1, the ceramic body 10 comprises a first component and a second component.

[0054] In the first component, the total mole count of barium, strontium, calcium, and the first trace element is 100%, and the proportions of strontium, calcium, and the first trace element are adjusted. Strontium and barium are generally used to adjust the Curie point, while calcium can be used as a grain refinement control agent for ceramic particles. In the second component, the total mole count of titanium, manganese, and the second trace element is 100%, and the proportions of manganese and the second trace element are adjusted. Manganese can adjust the degree of resistance jump.

[0055] Please refer to Comparative Example C1 and Examples E1 to E6. The main difference between Comparative Example C1 and Examples E1 to E6 lies in the ratio of strontium and calcium. The ratios of strontium and calcium in Examples E1 to E6 were adjusted to 20% and 4.5% or more, respectively, while the ratios of strontium and calcium in Comparative Example C1 were 15% and 3%, respectively. The results show that the volume resistivity (ρ) of Examples E1 to E6 can be significantly reduced to below 9.03 Ω·cm; the Curie point (Tc) is maintained between 85°C and 91°C; and the resistance jump rate (R125 / R25) is generally above 43. In contrast, the volume resistivity (ρ) of Comparative Example C1 is much higher than 10 Ω·cm, and the resistance jump rate (R125 / R25) is also lower.

[0056] Please refer to Examples E7 to E9 and Comparative Examples C2 to C3. The ratios of strontium and calcium in Examples E7 to E9 were maintained within the same range as in Examples E1 to E6, while the ratio of the second trace element was slightly increased. The main difference between Comparative Example C2 and Examples E7 to E9 is that the strontium ratio in Comparative Example C2 is slightly higher, at 30%. The main difference between Comparative Example C3 and Examples E7 to E9 is that the ratio of the second trace element in Comparative Example C3 is slightly higher, at 0.2%. The results show that Examples E7 to E9 maintained a low resistance state below 10 Ω·cm; the Curie point (Tc) was approximately around 90°C; and the resistivity jump rate (R125 / R25) was approximately above 40. In contrast, although the volume resistivity (ρ) of Comparative Example C2 was low, its Curie point (Tc) was too low, failing to meet the required protection temperature. As for Comparative Example C3, its volume resistivity (ρ) was too high, making it difficult for current to pass through even when the component was not operating.

[0057] Please refer to Examples E10 to E11 and Comparative Example C4. The main difference between Examples E10 to E11 and Comparative Example C4 lies in the proportion of manganese. The proportion of manganese in Examples E10 to E11 is 0.02% to 0.03%, while the proportion of manganese in Comparative Example C4 is higher, at 0.04%. The results show that Examples E10 to E11 have lower volume resistivity (ρ) and higher resistance jump rate (R125 / R25). The volume resistivity (ρ) of Comparative Example C4 is significantly higher, at 23.8 Ω·cm, which would affect the current flow of the protected device under normal operation.

[0058] Please refer to Example E12 and Comparative Example C5. The main difference between Example E12 and Comparative Example C5 lies in the proportion of the second trace element. The proportion of the second trace element in Example E12 is 0.03%, while the proportion of the second trace element in Comparative Example C5 is lower, at 0.01%. The results show that Example E12 still maintains a lower volume resistivity (ρ), while the volume resistivity (ρ) of Comparative Example C5 is too high.

[0059] Please refer to Examples E13 and Comparative Example C6. Compared with Examples E12 and Comparative Example C5, Examples E13 and Comparative Example C6 compared the effect of the second trace element at a lower manganese ratio (0.01%). The proportion of the second trace element in Example E13 was 0.04%, while the proportion of the second trace element in Comparative Example C5 was higher, at 0.05%. The results show that when the manganese ratio is 0.01%, a more ideal low volume resistivity (ρ) can be obtained with a second trace element ratio of 0.04%.

[0060] In the aforementioned sintering process, this invention further includes testing the adjustment of the oxygen content in the sintering atmosphere. Please refer to Table 2 and Figure 8.

[0061] Table 2 Group Composition percentage (mol%) Oxygen content (%) in sintering atmosphere Electrical characteristics heating phase High temperature section Cooling section Sr Ca R1 Mn R2 T1-T2 T2-T3 T3-T4 T4-T5 ρ (Ω.cm) Tc (℃) R125 / R25 E7 20 4.5 0.15 0.01 0.02 21% 21% 21% 21% 6.49 89 39.8 E10 20 4.5 0.15 0.02 0.02 21% 21% 21% 21% 7.89 88 56.5 E12 20 4.5 0.15 0.02 0.03 21% 21% 21% 21% 7.28 90 53.2 C7 20 4.5 0.15 0.01 0.02 3% 3% 3% 3% 1.53 - C8 20 4.5 0.15 0.02 0.02 3% 3% 3% 3% 1.03 - C9 20 4.5 0.15 0.02 0.03 3% 3% 3% 3% 1.26 - E14 20 4.5 0.15 0.01 0.02 10% 3% 15% 21% 2.88 86 16.6 E15 20 4.5 0.15 0.02 0.02 10% 3% 15% 21% 3.02 85 21.3 E16 20 4.5 0.15 0.02 0.03 10% 3% 15% 21% 3.35 86 19.6 E17 20 4.5 0.15 0.01 0.02 7% 3% 15% 21% 2.76 85 15.9 E18 20 4.5 0.15 0.02 0.02 7% 3% 15% 21% 2.89 86 18.6 E19 20 4.5 0.15 0.02 0.03 7% 3% 15% 21% 3.02 85 17.3 C10 20 4.5 0.15 0.01 0.02 3% 3% 5% 21% 3.02 82 6.3 C11 20 4.5 0.15 0.02 0.02 3% 3% 5% twenty one% 2.95 80 4.8 C12 20 4.5 0.15 0.02 0.03 3% 3% 5% twenty one% 2.86 83 6.4

[0062] As shown in Figure 8, the sintering time is 1 hour, and the main temperature points in the sintering process are T1, T2, T3, T4, and T5, corresponding to 500℃, 1320℃, 1320℃, 800℃, and 300℃, respectively. The temperature rise range is from 500℃ to 1320℃ (T1-T2); the high temperature range is from 1320℃ to 1320℃ (T2-T3); and the cooling ranges are from 1320℃ to 800℃ (T3-T4) and from 800℃ to 300℃ (T4-T5). In this experiment, it was found that adjusting the oxygen content could further reduce the volume resistivity (ρ) under the composition ratio of the aforementioned embodiments.

[0063] Please refer to Examples E7, E10, and E12 and Comparative Examples C7 to C9. In these groups, the same oxygen content was maintained in the heating, high-temperature, and cooling stages. The oxygen content of Examples E7, E10, and E12 was 21%, while the oxygen content of Comparative Examples C7 to C9 was 3%. The results show that the oxygen content in Comparative Examples C7 to C9 was too low, preventing the ceramic particles in the ceramic body 11 from forming a sufficient oxide layer to produce the characteristic of a resistance jump. Although the volume resistivity (ρ) was low, the lack of a resistance jump characteristic prevented it from functioning as an overcurrent protection element.

[0064] Please continue to refer to Examples E14 to E19 and Comparative Examples C10 to C12. In these groups, the oxygen content in the heating stage, the high-temperature stage, and the first part of the cooling stage (T3-T4) was adjusted to be below 21%, while the later part of the cooling stage (T4-T5) maintained a high oxygen content of 21%. More specifically, in Examples E14 to E19, the oxygen content in the heating stage, the high-temperature stage, and the first part of the cooling stage (T3-T4) showed a high-low-high trend, with the oxygen content in the heating stage all above 7% and the oxygen content in the first part of the cooling stage (T3-T4) being 15%. In contrast, in Comparative Examples C10 to C12, the oxygen content in the heating stage, the high-temperature stage, and the first part of the cooling stage (T3-T4) showed a low-low-high trend, with the oxygen content in the heating stage and the first part of the cooling stage (T3-T4) all below 5%. The results showed that the volume resistivity (ρ) of Examples E14 to E19 could be adjusted to be much lower than 10 Ω·cm; the Curie point was 85°C or 86°C; and the resistance jump rate (R125 / R25) was 15.9 to 21.3. In contrast, although Comparative Examples C10 to C12 had similar volume resistivity (ρ) and Curie point, their resistance jump rate (R125 / R25) was too low to produce a good current cutoff effect when the component was in operation.

[0065] Table 3 Group ceramic body Structural design Electrical characteristics source ρ (Ω.cm) Number of external electrode coverage areas Internal electrode width (mm) Inner electrode spacing (mm) resistance value (Ω) R125 / R25 E20 E12 7.33 2 0.151 0.45 398 22.7 E21 7.25 3 0.153 0.45 256 19.6 C13 7.28 5 0.148 0.45 332 20.4 E22 7.35 2 0.202 0.40 346 20.8 E23 7.32 3 0.205 0.40 219 18.5 C14 7.25 5 0.198 0.40 324 19.8 E24 E17 2.86 2 0.153 0.45 172 18.8 E25 2.90 3 0.146 0.45 113 16.4 C15 2.98 5 0.155 0.45 135 17.3 E26 2.93 2 0.197 0.40 134 17.5 E27 2.85 3 0.205 0.40 101 15.8 C16 2.84 5 0.208 0.40 141 16.3

[0066] In Table 3, the ceramic body 11 prepared above was tested with different structural designs. The number of external electrode coverage surfaces refers to the number of coverage surfaces of the external electrode layers 3 and 30 at one end of the component. For example, in Figure 2, the external electrode layer 30 covers the top surface 11, the first end surface 13, and the bottom surface 12, so the number of external electrode coverage surfaces is 3; in Figure 4, the external electrode layer 30 covers the top surface 11 and the bottom surface 12, so the number of external electrode coverage surfaces is 2; and in Figure 1a, the external electrode layer 3 covers all surfaces at one end, so the number of external electrode coverage surfaces is 5.

[0067] The inner electrode width refers to the width of the inner electrode layer at one end when viewed in cross-section, as shown by the width W in Figures 3a and 5a. The inner electrode spacing is the aforementioned spacing G.

[0068] The ceramic bodies of groups E20, 21, 13, 22, 23, and 14 are all the same as those in the aforementioned embodiment E12.

[0069] Please refer to Examples E20, E21, and Comparative Example C13. The inner electrode spacing in all groups was 0.45 mm, and the inner electrode width ranged from 0.148 mm to 0.153 mm. Results showed that, compared to conventional structural designs, the ceramic thermistor 100 of the first embodiment of the present invention (i.e., Example E21) exhibited a lower resistance value, while the ceramic thermistor 200 of the second embodiment of the present invention (i.e., Example E20) exhibited a better resistance jump rate (R125 / R25).

[0070] Please refer to Examples E22, E23, and Comparative Example C14. The inner electrode spacing in all groups was 0.4 mm, and the inner electrode width ranged from 0.198 mm to 0.205 mm. Similarly, the results show that, compared to conventional structural designs, the ceramic thermistor 100 of the first embodiment of the present invention (i.e., Example E23) can have a lower resistance value, while the ceramic thermistor 200 of the second embodiment of the present invention (i.e., Example E22) can have a better resistance jump rate (R125 / R25).

[0071] The ceramic bodies of groups E24, 25, 15, 26, 27, and 16 are all the same as those in the aforementioned embodiment E17.

[0072] Please refer to Examples E24, E25, and Comparative Example C15. The inner electrode spacing in all groups was 0.45 mm, and the inner electrode width ranged from 0.146 mm to 0.155 mm. Results showed that, compared to conventional structural designs, the ceramic thermistor 100 of the first embodiment of the present invention (i.e., Example E25) exhibited a lower resistance value, while the ceramic thermistor 200 of the second embodiment of the present invention (i.e., Example E24) exhibited a better resistance jump rate (R125 / R25).

[0073] Please refer to Examples E26, E27, and Comparative Example C16. The inner electrode spacing in all groups was 0.4 mm, and the inner electrode width ranged from 0.197 mm to 0.208 mm. Similarly, the results show that, compared to conventional structural designs, the ceramic thermistor 100 of the first embodiment of the present invention (i.e., Example E27) can have a lower resistance value, while the ceramic thermistor 200 of the second embodiment of the present invention (i.e., Example E26) can have a better resistance jump rate (R125 / R25).

[0074] In summary, the ceramic thermistor of the present invention can be designed to have low volume resistivity, suitable Curie point, and good resistance jump rate. Furthermore, the electrical properties can be further improved by adjusting the material composition of the ceramic body.

[0075] The technical content and features of this invention have been disclosed above. However, those skilled in the art may still make various substitutions and modifications that do not depart from the spirit of this invention based on the teachings and disclosures of this invention. Therefore, the scope of protection of this invention should not be limited to what is disclosed in the embodiments, but should include various substitutions and modifications that do not depart from this invention, and is covered by the following claims.

[0076] 1, 10: Ceramic body 11: Top surface 12: Bottom surface 13: First end face 14: Second end face 15: First side view 16: Second side view 2, 20: Inner electrode layer 21: Top surface of the inner electrode 22: Bottom surface of internal electrode 23: First sidewall 24: Second sidewall 3, 30: Outer electrode layer 40: Insulation layer 100, 200: Ceramic thermistor G: Spacing W: Width

Claims

1. A ceramic thermistor, comprising: a ceramic body having a positive temperature coefficient, and including a top surface, a bottom surface, a first end surface, a second end surface, a first side surface, and a second side surface opposite to the first side surface, wherein the top surface and the bottom surface are disposed opposite to each other, the first end surface and the second end surface are disposed opposite to each other and connected to the top surface and the bottom surface, and the first side surface and the second side surface connect the top surface, the bottom surface, the first end surface and the second end surface, thereby forming a hexahedron; an inner electrode layer disposed at both ends of the top surface, wherein the inner electrode layers at both ends are separated by a gap, wherein the inner electrode layer has an inner electrode top surface and a first sidewall, wherein the inner electrode top surface is parallel to the top surface of the ceramic body, and the first sidewall extends vertically from the inner electrode top surface to the top surface; An insulating layer covers the top surface of the ceramic body, wherein the insulating layer is disposed within the spacing of the inner electrode layers at both ends and extends to the first sidewall of the inner electrode layer; and an outer electrode layer covers the inner electrode layer and extends to cover the first end face and the second end face of the ceramic body, but does not cover the first side face and the second side face of the ceramic body, thereby the outer electrode layer partially covers the insulating layer and the first sidewall of the inner electrode layer.

2. The ceramic thermistor of claim 1, wherein the insulating layer completely covers the first sidewall of the inner electrode layer and extends further to the top surface of the inner electrode, thereby the outer electrode layer partially covers the insulating layer and the top surface of the inner electrode.

3. The ceramic thermistor of claim 1, wherein the insulating layer further covers the bottom surface, the first side surface and the second side surface of the ceramic body, such that only the insulating layer and the outer electrode layer of the ceramic thermistor are exposed to the external environment.

4. The ceramic thermistor according to claim 1, wherein the spacing is 0.4 mm to 0.45 mm.

5. The ceramic thermistor of claim 1, wherein the inner electrode layer has a width extending toward the first end face and the second end face, and the width is 0.15 mm to 0.21 mm.

6. The ceramic thermistor of claim 1, wherein the material of the inner electrode layer does not contain titanium.

7. The ceramic thermistor of claim 6, wherein the material of the inner electrode layer is selected from the group consisting of nickel, chromium, nickel-chromium alloys, nickel-copper alloys, silver, aluminum, and combinations thereof.

8. The ceramic thermistor element according to claim 1, wherein the ceramic body comprises a first component and a second component, wherein: The first component comprises barium, strontium, calcium and a first trace element; the second component comprises titanium, manganese and a second trace element; the first trace element and the second trace element are selected from the group consisting of ytterbium, lanthanum, cerium, antimony, tungsten, neodymium, samarium, europium, thorium, tantalum, erbium, thionium and combinations thereof; and the volume resistivity of the ceramic body is less than 10 Ω·cm.

9. The ceramic thermistor of claim 8, wherein the total mole count of barium, strontium, calcium and the first trace element is 100%, and: strontium accounts for 20% to 25%; calcium accounts for 4.5% to 5%; and the first trace element accounts for 0.13% to 0.17%, thereby the Curie temperature of the ceramic body is 85°C to 91°C.

10. The ceramic thermistor of claim 8, wherein the total mole count of titanium, manganese and the second trace element is 100%, and: manganese accounts for 0.01% to 0.03%; and the second trace element accounts for 0.02% to 0.04%.

11. The ceramic thermistor according to claim 10, wherein: The ceramic body has a first resistance value at 25°C; the ceramic body has a second resistance value at 125°C; And the ratio of the second resistance value to the first resistance value is 10 or more.

12. A ceramic thermistor, comprising: a ceramic body having a positive temperature coefficient characteristic, and including a top surface, a bottom surface, a first end surface and a second end surface, wherein the top surface and the bottom surface are disposed opposite to each other, and the first end surface and the second end surface are disposed opposite to each other and connected to the top surface and the bottom surface; an inner electrode layer disposed at both ends of the top surface, wherein the inner electrode layers at the two ends are separated by a gap; and an outer electrode layer covering the inner electrode layer and the top surface of the ceramic body, and not extending to the first end surface and the second end surface.

13. The ceramic thermistor of claim 12, wherein the ceramic body further includes a first side surface and a second side surface opposite to the first side surface, connecting the top surface, the bottom surface, the first end surface and the second end surface, thereby forming a hexahedron, wherein the outer electrode layer does not cover the first side surface and the second side surface.

14. The ceramic thermistor of claim 13 further includes an insulating layer covering the top surface of the ceramic body, wherein the insulating layer is disposed within the spacing of the inner electrode layers at both ends.

15. The ceramic thermistor of claim 14, wherein the inner electrode layer has an inner electrode top surface and a first sidewall, wherein: The top surface of the inner electrode is parallel to the top surface of the ceramic body, and the first sidewall extends vertically from the top surface of the inner electrode to the top surface; and the insulating layer extends to the first sidewall, thereby the outer electrode layer partially covers the insulating layer and the first sidewall.

16. The ceramic thermistor of claim 15, wherein the insulating layer completely covers the first sidewall of the inner electrode layer and extends further to the top surface of the inner electrode, thereby the outer electrode layer partially covers the insulating layer and the top surface of the inner electrode.

17. The ceramic thermistor of claim 14, wherein the inner electrode layer has an inner electrode top surface and a first sidewall, wherein: The top surface of the inner electrode is parallel to the top surface of the ceramic body, and the first sidewall extends vertically from the top surface of the inner electrode to the top surface; the outer electrode layer covers the first sidewall of the inner electrode layer and the top surface of the inner electrode; and the insulating layer extends to the outer electrode layer, and further extends parallel to the first sidewall and covers the outer electrode layer.

18. The ceramic thermistor of claim 14, wherein the insulating layer further covers the bottom surface, the first side surface, the second side surface, the first end surface, and the second end surface of the ceramic body.

19. The ceramic thermistor of claim 12, wherein the spacing is 0.4 mm to 0.45 mm.

20. The ceramic thermistor of claim 12, wherein the inner electrode layer has a width extending toward the first end face and the second end face, and the width is 0.15 mm to 0.21 mm.

21. The ceramic thermistor of claim 12, wherein the material of the inner electrode layer does not contain titanium.

22. The ceramic thermistor of claim 21, wherein the material of the inner electrode layer is selected from the group consisting of nickel, chromium, nickel-chromium alloys, nickel-copper alloys, silver, aluminum, and combinations thereof.

23. The ceramic thermistor of claim 12, wherein the ceramic body comprises a first component and a second component, wherein: The first component comprises barium, strontium, calcium and a first trace element; the second component comprises titanium, manganese and a second trace element; the first trace element and the second trace element are selected from the group consisting of ytterbium, lanthanum, cerium, antimony, tungsten, neodymium, samarium, europium, thorium, tantalum, erbium, thionium and combinations thereof; and the volume resistivity of the ceramic body is less than 10 Ω·cm.

24. The ceramic thermistor of claim 23, wherein the total mole number of barium, strontium, calcium and the first trace element is 100%, and: strontium accounts for 20% to 25%; calcium accounts for 4.5% to 5%; and the first trace element accounts for 0.13% to 0.17%, thereby the Curie point of the ceramic body is 85°C to 91°C.

25. The ceramic thermistor of claim 23, wherein the total mole count of titanium, manganese and the second trace element is 100%, and: manganese accounts for 0.01% to 0.03%; and the second trace element accounts for 0.02% to 0.04%.

26. The ceramic thermistor according to claim 25, wherein: The ceramic body has a first resistance value at 25°C; the ceramic body has a second resistance value at 125°C; And the ratio of the second resistance value to the first resistance value is 10 or more.

27. A ceramic thermistor, comprising: a ceramic body having a positive temperature coefficient, and including a top surface, a bottom surface, a first end surface, a second end surface, a first side surface, and a second side surface opposite to the first side surface, wherein the top surface and the bottom surface are disposed opposite to each other, the first end surface and the second end surface are disposed opposite to each other and connected to the top surface and the bottom surface, and the first side surface and the second side surface connect the top surface, the bottom surface, the first end surface and the second end surface, thereby forming a hexahedron; an inner electrode layer disposed at both ends of the top surface, wherein the inner electrode layers at both ends are separated by a gap, wherein the inner electrode layer has an inner electrode top surface and a first sidewall, wherein the inner electrode top surface is parallel to the top surface of the ceramic body, and the first sidewall extends vertically from the inner electrode top surface to the top surface; An outer electrode layer covers the first sidewall of the inner electrode layer and the top surface of the inner electrode, wherein the outer electrode layer extends and covers the first end face and the second end face, but does not cover the first side face and the second side face; and an insulating layer covers the top surface of the ceramic body, wherein the insulating layer is disposed within the gap between the two ends of the inner electrode layer, and the insulating layer extends to the outer electrode layer, and further extends parallel to the first sidewall of the inner electrode layer and covers the outer electrode layer.

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