STATIC INDUCTION THYRISTOR (SITH)

STATIC INDUCTION THYRISTOR (SITH)

INTRODUCTION The static induction thyristor (SITh) or field-controlled diode (FCD) was first introduced by Teszner Teszner in the 1960’s. This device is capable of conducting co nducting large currents with a low forward voltage and turn-off quickly. It is a self-controlled GTO-like on-off on-o ff device that was commercially c ommercially introduced by Toyo Electric Co. (Toyo (Toyo Denki) of Japan in 1988. It belongs to a family family of Static Induction Device and is a high power high frequency power semiconductor device.

It is essentially a p+nn+ diode with a buried p+ grid like gate structure. The device structure is analogous to SIT except that a p+ layer has been added to the anode side.

Fig. 1

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Static induction devices There are many devices which belong to the static induction devices family:   

Static Induction Transistor (SIT), Static Induction Diode (SID), Static Induction Thyristor,

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Static Induction Transistor Logic (SITL),

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Static Induction MOS Transistor (SIMOS)


Features 

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Since they are normally on-state, gate electrodes must be negatively biased to hold off-state. The SI-thyristor at on-state behaves s imilar imilar to pin diodes. The on-state voltage is low in the Si-thyristor, Si -thyristor, which is due to thyristor t hyristor action followed by carrier injection effect around the gate channel. Minority-carrier device (a JFET structure with an additional add itional injecting layer).

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Power-handling capability similar to GTO.

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Faster switching speeds than GTO.

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Level-triggered and Voltage-driven (voltage-controlled) devices.

Fabrication Many interesting works have been done on fabricating different structures character istics , such as of SITH to improve its forward blocking and switching characteristics anode-shorting pattern , shallow-junction pattern and double-gate pattern.

Fig. 3 Surface plan view of the fabricated SI thyristor

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BASIC STRUCTURE OF SITH

Fig. 4 

Basic structural types of SITH had been developed in recent years, such as buried gate, surface gate, recessed gate, double dielectrics gate and buried-gate with diffused diffused source region (DSR buried-gate). a node is positive and the gate  It is normally ON state device, i.e if the anode voltage is zero, the device will behave like a diode and current will flow freely. +  The forward biasing of the P N junction will cause a hole injection into the region N region and its conductivity will be modulated.  When the gate is reversed biased with respect to cathode, a depletion layer will block Anode current. As a results device gets OFF.  Evidently it is not a thyristor like structure like trigger into conduction device but somewhat SIT like V-I characteristics with with varying Negative gate biase.

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WORKING ON-STATE

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When a positive voltage pulse is applied to the gates, the depletion region is filled with carriers and the device becomes on-state. The transition time of the turn-on process is largely dominated by the rate of the carrier injection time. At the turn-on phase the SI-thyristor acts just like as a pin-diode

OFF-STATE

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Since SITh is normally ON state, the gate electrodes have to be negatively biased. The negative bias voltage to the gate forms a low-conductive depletion region around the gates and the SI-thyristor holds off-state.

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Some examples

Type

4kV/300A

4kV/600A /400A

5.5kV/600A /400A

4kV/30A

Package

Ceramics Sheered type

Ceramics Sheered type (Reverse Conducting)

Ceramics Plastic Mold Sheered type type (Reverse Conducting)

Inverter (Soft Switching)

Pulsed power

Outside view

Applications Inverter Pulsed power

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Pulsed power Inverter


ADVANTAGES AND DISADVANTAGES

Advantages of SITh 

The device has also high immunity for electromagnetic noise.

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SITh has high di/dt and dv/dt critical cr itical ratio. capable of handling rapid voltage or current changes.

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It’s a vertical structure device with short mul tichannel. Being a vertical device, the SITh offers advantages in obtaining higher breakdown voltages than FET.

Disadvantages 

One of the disadvantages of the t he SIT is the relatively flat shape of the potential barrier. This This leads to slow, diffusion based based transport of carriers in the vicinity of the potential barrier.

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SPECIFICATIONS •

Short channel length

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Low gate series resistance

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Low gate source capacitance

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Small thermal resistance

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Low noise

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High audio frequency power capability capab ility

• The forward blocking voltage of this SITH has been increased to 1600 V from the previous value of 1000 V, •

The blocking gain increased from 40 to 70,

• A high anode blocking voltage VAK and switching speed are necessary parameters for SITH with good performance performance.

Applications Due to its high switching speed, high di/dt and dv/dt capabilities, along with a low forward on state voltage (Von), SITH has been used in systems of energy accelerator, current-source inverter and high-frequency high- frequency power conversion, etc.

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References 

www.wikipedia.org

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“Present status of SIThy” shimizu,sekiya,Iidal NGK insulators

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“Power electronics handbook” by M.Rashid

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“Recent development of the SIThy and its applications”

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Evaluation of Modern Power Semiconductor Devices and Future Trends of Converters by Bimal K. Bose, F ell ow, ZEEE

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STATIC INDUCTION THYRISTOR (SITH)

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