JPH025006B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high dielectric thin film capacitor that is small in size and has a large capacitance. As electronic devices become smaller, the number of electronic components housed per unit volume is increasing. Boundary-related elements such as transistors and diodes have become extremely miniaturized due to advances in integrated circuit fabrication technology, but capacitors, on the other hand, have a characteristic that capacitance is directly proportional to electrode area, so it is difficult to reduce capacitance. It is not easy to downsize without In particular, miniaturization of capacitors with a capacitance of 1 μF or more has been slow. There are three ways to downsize a capacitor without reducing capacitance. One is to increase the dielectric constant of the dielectric. Materials with large dielectric constants include oxides such as _TiO2 ,
Examples include ferroelectric materials such as BaTiO ₃ . Capacitors using such a high dielectric material have traditionally existed as ceramic capacitors, but these are made by turning the high dielectric material into a slurry with an organic binder, etc.
The method used is to spread the material thinly and sinter it, and because it contains many voids inside, it does not fully demonstrate the characteristics of the material. Further, as described below, it is insufficient to reduce the thickness, which is a factor in reducing the size of the capacitor. Another way to downsize capacitors is to reduce the thickness of the base material that makes up the electrodes. This method is expected to have the effect of reducing the volume occupied by the electrode.

Another method is to reduce the thickness of the dielectric. This method not only has the effect of reducing the volume occupied by the dielectric, but also has the effect of increasing the capacitance for the same electrode area.In other words, to make the capacitance the same, the electrode area must be reduced. There is an effect that can be done. However, the latter two methods of reducing the thickness of the structure not only make it difficult to manufacture such a thin structure, but also require a special method in the process of processing it into a capacitor, and are difficult to handle. It becomes difficult. In other words, this method is unavoidably adopted in order to increase the capacitance, and it is desirable if the capacitance can be reduced without reducing the capacitance by using a material with a thickness that is easy to handle.

In view of this situation, the present inventor conducted extensive research to develop a compact capacitor with a large capacitance, and as a result, arrived at the present invention. That is, in a capacitor in which the electrode is a metal foil and the dielectric is a high dielectric thin film, the surface of the metal foil serving as the electrode of the capacitor is coated under a reduced pressure of 1×10 ^-1 Torr or less.
It has been discovered that a capacitor composed of a high dielectric thin film laminated metal foil obtained by laminating high dielectric thin films with a thickness of 0.01 to 1 micron satisfies the object of the present invention. be.

Any metal foil serving as the electrode in the present invention may be used as long as it is a good electrical conductor, but aluminum foil is most suitable because it is easily available and inexpensive. As mentioned above, the thinner the metal foil, the better for miniaturization, but in the process of laminating high dielectric thin films, processing into capacitors, etc., in the case of aluminum foil, it is necessary to reduce the thickness to 20 microns or less. , it was broken and wrinkled, making it extremely difficult to work with. In other words, the purpose of the present invention is to use a metal foil with a thickness that is easy to handle. The surface of the metal foil is preferably smooth in order to improve adhesion to the counter electrode.

Examples of the high dielectric material in the present invention include oxides of Ti and Ta, and ferroelectric materials such as BaTiO ₃ .
Methods for laminating these high dielectric materials on metal foil to a thickness of 0.01 to 1 micron under reduced pressure of 1×10 ^-1 Torr or less include vacuum evaporation, sputtering, ion plating, and low pressure CVD. ,
There are plasma CVD methods, etc. The reason for laminating the layers under reduced pressure of 1×10 ^-1 Torr or less is to prevent voids from forming in the laminated high dielectric thin films. This is also to prevent the formation of an oxide film on the foil itself. All of the above-mentioned lamination methods are suitable for forming a thin film under such reduced pressure conditions. As a high dielectric material, BaTiO ₃ in which part of the Ba is replaced with a metal such as Sr has a dielectric constant of over 10,000 at room temperature, and is extremely effective in miniaturizing capacitors. When laminating such high dielectric thin films, it is desirable to use a high frequency sputtering method using a high dielectric material microcrystallized by sintering as a target. In particular, the magnetron-based high-frequency sputtering method is most suitable for production because it can form a thin film at a high speed. The thickness of the dielectric layer may be appropriately selected depending on the capacitance and withstand voltage required for the intended capacitor. Although it is preferable to make it thin for miniaturization, a thickness of 0.01 micron or less is practically meaningless because not only the withstand voltage decreases but also the frequency of pinholes increases.
Further, since the high dielectric material has brittle properties, a thickness of 1 micron or more is not preferable in order to use the laminate in the form of a roll. As an example, the high dielectric thin film laminated metal foil prepared in this way is processed into a capacitor as follows. As shown in Fig. 1, a metal foil 4 is layered as a counter electrode on a laminate 3 in which a high dielectric thin film 2 is laminated on a metal foil 1, lead wires 5 and 5' are attached, and the whole is sealed with a resin 6. do. Further, as shown in FIG. 2, the high dielectric thin film 8 of the laminate 7
A conductive paint 9 is applied to the surface of the device, a lead wire 10 is attached with a conductive adhesive 11, and the whole is sealed with a resin 12. Also, as shown in Figure 3,
A large number of laminates 13 are stacked one on top of the other with slight shifts alternately, and electrode extraction parts 14, 14' and lead wires 15, 15' are attached to the shifted parts and sealed with resin 16. It is also possible to use two long tape-like laminates in a rolled-up configuration as shown in FIG. 3, in which they are overlapped.

Examples are given below.

Example 1 TiO ₂ was placed on aluminum foil with a thickness of 25μ and a smooth surface.
was deposited on one side to a thickness of 0.05 micron using an electron beam heating vacuum evaporation device. Since oxygen in the composition of the deposited film had decreased, the laminate was heated in air at 300° C. for 5 hours to adjust the composition. A capacitor was fabricated by stacking 50 layers of this laminate as shown in Figure 3. The size of the capacitor was 1.3 mm thick, 3.0 mm wide, and 5.0 mm deep, and the electrode area was 6.5 cm ² . The capacitance of this capacitor was 4.0 μF.

Example 2 Using a target made of BaTiO ₃ ceramic with a dielectric constant of 18,000 at room temperature on an aluminum foil with a thickness of 50 μm and a smooth surface, a dielectric layer with a thickness of 0.1 μm was formed using a magnetron high-frequency sputtering device. were laminated. As shown in Figure 2, this laminate is
A capacitor was made using conductive paint.
The size of the capacitor is 0.2mm thick, 3.0mm wide,
The depth was 10.0 mm, and the electrode area was 0.3 cm ² .
The capacitance of this capacitor was 80 μF.
Note that a capacitor of this shape is used standing up on a circuit board, and in that case, the area occupied by the board is 0.6 mm ² .

[Brief explanation of drawings]

1 and 2 are cross-sectional views of a capacitor using one high dielectric thin film laminated metal foil according to the present invention, and FIG. 3 is a cross-sectional view of a capacitor using a large number of high dielectric thin film laminated metal foils.

Claims (1)

[Claims] 1. A high dielectric thin film capacitor characterized by laminating a high dielectric thin film with a thickness of 0.01 to 1 micron at a reduced pressure of 1×10 ^-1 Torr or less on the surface of a metal foil serving as an electrode.