［ Vacuum Equipment ］

Vacuum Capacitor ( VC)

Keywords

Toshinori Tatsumi,
Takuya Shimokawa,Yuichi Nishikiori

Vacuum, Capacitor, Variable, Motor-powered, High frequency, RF, Vacuum insulation, High accuracy, Temperature stability

Abstract

We have been developing and manufacturing Vacuum Capacitors (VCs)
since 1992 as the one and only VC supplier in Japan. In making VCs, we adopt
the technologies and know-hows related to Vacuum Interrupter (VIs) that weaccumulated as we develop and manufacture VIs and Vacuum Circuit-Breakers(VCBs) for more than half a century. Our VCs are used as an embedded productfor Radio Frequency (RF) power supply for the plasma generation of thin ﬁlm
manufacturing equipment and control circuit devices for thin ﬁlm equipment(vacuum process equipment for the deposition and modiﬁcation of thin ﬁlms.)
Our VCs are contributing to the manufacture of semiconductors, Flat Panel
Displays (FPDs) and Solar Panels. Our VCs come in Fixed Vacuum Capacitors(FVCs), Variable Vacuum Capacitors (VVCs), and Auto tuning Vacuum Capacitors(Auto-VCs). The Auto-VCs adopt the module design where motor and control
systems necessary for static capacitance control, are put together in a module.
Using our own unique technologies, we are able to commercialize two types ofVCs; one that features the double bellows realizing a low torque, and the otherwith the ball screw, which is applicable to high-speed control and long-lastinguse. In addition, we realized capacitance tolerance rate of ±1% and a compact
design. We provide VCs that meet various needs of our customers.

1 Preface
For more than half a century, we have beendeveloping and manufacturing Vacuum Interrupters(VIs) and Vacuum Circuit-Breakers (VCBs), whichapplied for railway facilities and high-voltage substations.
By using the knowledge that we accumulated
as we developed VIs and VCBs, we started to develop Vacuum Capacitors (VCs) in 1992, and succeeded in manufacturing in 1994. Since, we havecontinued developing and manufacturing varioustypes of highly reliable VCs as the one and only
supplier of VCs in Japan. Major application ﬁeldsof VCs are manufacturing equipment of semiconductors, Flat Panel Displays (FPDs), and SolarPanels. Our VCs are used as an embedded productfor Radio Frequency (RF) power supply for thegenerating plasma of thin ﬁlm equipment (vacuum
process equipment for the deposition and modiﬁcation of thin ﬁlms) and control circuit device forthin ﬁlm equipment.

They are also used in various areas of broadcasting communication equipment, analytical equipment for mass analysis or X-ray inspection, forresearch facilities such as accelerators, and for
induction heating equipment or CO2 laser machines.
It can be said that our VCs support the RF energy
power supply of various industrial equipment. This
article introduces the major features of our VCs.

2 Trends of Development
In the recent semiconductor industry, theCentral Processing Unit (CPU) and the MicroProcessing Unit (MPU) earned better performanceand greater capacity of memory. As we mentioned,semiconductor manufacturing equipment is required
to ﬁt into nano-level processing, and to perform frequent processing for multilayer structure. The VCs
are required to speed up accordingly. Meanwhile,in the ﬁeld of FPD, the screen image quality ofsmartphones is improved like the High DynamicRange (HDR) Organic Light-Emitting Diode (OLED)MEIDEN REVIEW Series No.177 2019 No.3

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Screw actuator
shaft

panel and the screen sizes of FPD TVs and digital
signages are increasing in size. The size of glass
has been expanded in proportion (10.5th generation: 2940 × 3370mm). Consequently, accuracy levelof the manufacturing equipment has gotten higher
and screen areas have been enlarged. Accordingly,
the VCs are required to secure higher accuracy,higher withstand voltage, and larger current carrying capability.
To meet these requirements, we recently developed the ball-screw VC with a capability of highspeed control, the Auto tuning Vacuum Capacitors(Auto-VCs), the Fixed Vacuum Capacitors (FVCs) thatassures a high accuracy of capacitance tolerance
rate of ±1%, and the Vacuum Variable Capacitors(VVCs), which its current capacity is 400Arms.

3 What is a VC?
The VC is a capacitor with the electrode gap ina vacuum. Fig. 1 shows the internal structure of
the Meiden VCs. Unlike ceramic capacitors whereelectric charges are stored by inserting a dielectric
substance in the electrode gap, dielectric loss canbe eliminated by the effect of a vacuum.
It becomes a small and high withstand voltage
capacitor by keeping vacuum insulation. The current capacity of VCs is therefore, more than
100Arms, and the withstand voltage of VCs is a
one-tenth than the atmosphere distance by the vacuum insulation, so a large current can be suppliedin a compact size. In addition, VCs have the superior temperature stability among capacitors, and thecapacitance characteristic is almost not affected byexternal environmental changes such as temperature, humidity, and dirt.
Further, among the types of VCs, there are
VVCs in which the capacitance can be adjusted bybellows that expands and contracts while sealing avacuum. For example, VVCs can adjust capacitance of more than a ﬁgure like 1500pF from 10pF.
This is a function that can adjust the impedancecontinuously, which other capacitors do not have forhigh voltage applications. VVCs were, therefore,
used in the past for the channel adjustment ofbroadcast equipment. In recent years, it is being
used for plasma control – it especially ﬁts for RF
technology application which controls high frequency energy of kW class or more. From now on, it isexpected to be applied to wireless power transfer
for EV/PHV.

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Guide bearing
Bellows (forvacuum sealing)
Bellows (forcurrent carrying)
Ceramic envelope
Movable Electrode
Fixed Electrode

VP Series (Double bellows)

Screw actuator
shaft

Guide bearing
Upper flange

Ceramic envelope

Upper electrode

Bellows (forvacuum, current)

Ceramicenvelope
Lower flange

Movable Electrode

Lower electrode

Fixed ElectrodeFH Series (Large current type)

UW Series(Low loss, high-strength bellows)

Screw actuator
shaft
Max. stopper screw
Bellows (forvacuum, current)

Upper flange
Upper electrode
Center pin

Ceramic envelope

Ceramicenvelope

Center pin
Movable Electrode

Lower electrode

Fixed Electrode

Lower flange

FS･FC Series (Compact type)

VM Series (The first model)(a) Fixed type(b) Variable typeFig. 1

Internal Structure of Meiden VCs

There are FVCs of a ﬁxed type and VVCs of variable type in VCs.
The VVCs have bellows that expand and contract while sealinga vacuum for current carrying.

In the ﬁeld where the VC is used, any one of
the following items is indispensable:( 1) Power supply frequency is Radio frequency
form several 100kHz to several 100MHz( 2 ) Electric power is more than kW class( 3 ) High withstand voltage is kV class( 4 ) Temperature characteristic is less than 100ppm/℃( 5 ) Dispersion in capacitance is less than ±5%

4 Our VC Products
In manufacturing VCs, we adopt the vacuum
sealing brazing method inside the vacuum furnaceand does not have an exhaust pipe. This method
can perform brazing, vacuum exhaust and baking at

the same time; therefore, it is superior in mass-production.
In addition, by drawing on the experience wegained through the development of longer-life vacuum products, such as VIs and VCBs for more thanhalf a century, we could realize more than 20 yearsof the vacuum vessel life of the VCs.
Our VCs come in FVCs (the ﬁxed type), theVVCs (the variable type), and the Auto-VCs (themotorized variable type). The Auto-VCs adopt themodule design where the motor and control systems necessary for static capacitance control are
put together in a module.
Our FVCs have mainly two series. There is theFS series which realizes the compact design by thecenter pin and the other is the FH series that features permissible current of 100Arms or more and ahigh withstand voltage of 30kV0-p or more. The FH
series realized a high accuracy level by the uniqueelectrode manufacturing technology and dispersion
in capacitance is less than ±1% (usually ±5 to10%.)
Our VVCs are consisted of three series. Theﬁrst one is the VM series, which is our ﬁrst releasedmodel of our all VCs series. We adopted highstrength stainless steel copper-plated bellows thatoffers both vacuum sealing and current carrying.
Other adoption is a center pin that realized keeping
the insulation distance between the electrodes anda sliding in vacuum. The product life of the VM
series has dramatically improved compared to theinitial development stage. The second one is theUW series which achieved a compact design byusing our proprietary electrode manufacturing technology. The last one is the VP series which has adouble bellows structure where the bellows aredivided into one for vacuum sealing and the otherfor current carrying. This structure design enable torealize low torque and high current capacity.
Furthermore, our VCs support ball screws andDLC coated screws that meet the demand for highspeed control and long life. Fig. 2 shows the external appearance of the ball screw VC.
For the Auto-VC, we measure the capacitanceat the time when we ship our product from factory.
By calibrating the capacitance setting command,
we realized the capacitance setting accuracy levelof ±0.5% or less (These of typical VVCs are ±5%.)In addition, when customers adopt VVCs, they will
face issues such as shape of connection between(a) VH65-B typeFig. 2(b) UW65-B type(c) C82HE-B type

Ball Screw TypeThe VVCs with ball screw are shown. They are designed to meetthe requirements of high speed control and long-life operation.

Fig. 3Auto-VCs

Auto-VCs are shown. Auto-VCs are the product which
modularized VVCs, a motor, and a controller. This product cancontrol highly precise capacitance with less than ±0.5%.

VVCs and motor, and motor control. By preparing
the suitable shape and motor control, the development period of the customerʼs system has beenshortened. Fig. 3 shows the external appearance ofAuto-VCs.

5 Postscript
Our VCs may not be widely known, but they
cover the impor tant part, essential to the productionof the semiconductor and FPD manufacturing.
Without VCs, smartphones and FPD TVs cannot
be mass-produced.
We are going to continue to fulﬁll our customersʼ needs and we will work for the VCsʼ greater performance and convenience. We hope our development of VC products will give the best experiences
to our customers.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.

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