Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Patent
1990-09-28
1991-12-24
Griffin, Donald A.
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
29 2542, 501135, H01G 412, H01G 700, C04B 3546
Patent
active
050758187
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a semiconductor-type laminated ceramic capacitor with a grain boundary-insulated structure and a method for producing the same, and more particularly to a ceramic capacitor which absorbs low voltage noises and high frequency noises under the normal operational conditions as a capacitor, works as a varistor against invading high voltage loads such as pulses and electrostatic charges, thereby protecting built-in semiconductors and electronic equipment from being damaged by abnormal voltage loads such as noises, pulses and electrostatic charges arising from surrounding electronic equipment, wherein characteristics of said ceramic capacitor being stable to temperature changes.
BACKGROUND ART
Recently, semiconductor elements such as IC and LSI are widely used in electronic devices and equipment to realize multifunctional applications of the equipment and to make the equipment light, small and handy. However, the use of many semiconductor elements makes the electronic device less resistant to disturbance from electric noises. The conventional method to protect the electronic devices from invading electric noises is to integrate by-pass capacitors such as film capacitor, laminated ceramic capacitor and semiconductor ceramic capacitor into the power line of IC and LSI. These capacitors display excellent performances to absorb low voltage noises and high frequency noises. They are, however, so impotent to high voltage pulses and electrostatic charges that mulfunctionings of the equipment, break-down of semiconductors and/or capacitors themselves occur frequently when the electronic equipment is invaded by high voltage pulses or electrostatic charges. Therefore, these technical problems in the conventional capacitors should be improved.
A new type capacitor, which has sufficient resistance and excellent absorbing ability to pulses as well as good noise absorbing ability and stability to temperature and frequency changes, was developed and disclosed in Japanese Laid-Open Patent Publication No. 57-27001 and Japanese Laid-Open Patent Publication No. 57-35303 etc., wherein varistor functions were added to a ceramic capacitor made of SrTiO.sub.3 series of ceramic materials and the capacitor was defined as "a semiconductor type ceramic capacitor having varistor functions" (hereinafter referred to as a ceramic capacitor with varistor functions). This ceramic capacitor with varistor functions works as a varistor when high voltage pulses and electrostatic charges invade while it absorbs low voltage noises and high frequency noises as a conventional capacitor, thereby protecting the electronic equipment and built-in semiconductors from abnormal high voltage noises, pulses and electrostatic charges generated by surrounding electronic equipment and devices, and providing wide application fields of the capacitor.
Since the electronic parts are made more sophisticated, lighter and smaller, and more handy, ceramic capacitors with varistor functions are also required to be smaller but higher in performance. The effective electrode area of the conventional single-plate type ceramic capacitor with varistor functions will be, however, decreased when the capacitor is miniaturized, resulting in the reduction of electric capacitance and hence inferior reliability of the capacitor. A capacitor having laminated structure of the electrode is devised to solve the aforementioned problem, wherein the effective electrode area is expected to be increased. However, the ceramic capacitor with varistor functions is conventionally manufactured by a process comprising a step of coating the surface of a SrTiO.sub.3 type semiconductor element with oxides, followed by a thermal diffusion process to form an electric insulating layer in the grain boundaries. It is recognized to be very difficult to manufacture "a laminate type ceramic capacitor having varistor functions" (hereinafter referred to as a laminated ceramic capacitor with varistor functions) by sintering the material of the ceramic capacitor
REFERENCES:
patent: 499398 (1991-02-01), Huang et al.
patent: 4101454 (1978-07-01), Kulwicki et al.
patent: 4660017 (1987-04-01), Momoki et al.
patent: 4799127 (1989-01-01), Ono et al.
patent: 4977485 (1990-12-01), Mori et al.
Kobayashi Kimio
Okamoto Kaori
Takami Akihiro
Ueno Iwao
Wakahata Yasuo
Griffin Donald A.
Matsushita Electric - Industrial Co., Ltd.
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