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Posted on 01 June 2020

Power Devices Produced Using Proton Irradiation Technology

The application of proton irradiation technology has made possible the production of a new series of fast thyristors. These semiconductors have remarkably small turn-off time, small recovered charge and peak reverse recovery current.

Implantation of hydrogen atoms during proton irradiation helps to build local hidden n’-layers with low specific resistance inside the n--layer of the semiconductor element. This opens possibilities of using such hidden layers to produce power diode-thyristors (dynistors) and semiconductor voltage suppressors with increased power capacity.

 

Below is a description of devices produced using proton irradiation technology.

Fast Thyristors with Small Reverse Recovery Charge

Fast thyristors produced using proton irradiation technology exhibit the following key features:

1.      Lifetime control by proton irradiation of cathode side of thyristor element: The region of proton path termination in the silicon element is located close to the anode p-n junction. The lifetime close to the anode p-n junction (ta) can be in this case 2x to 3x less than the lifetime close to collector p-n junction (tc). Such an axial lifetime profile allows optimization of the relationship between VTM and Qrr: a 1.5x to 2x reduction of the Qrr value at the same VTM value is possible by using this axial profile instead of a traditional uniform profile.

2.      Dense grid of cathode short elements: Cathode shorts are distributed within the emitter area and the next elements are located at a distance of about 400 µm. Such a cathode short grid allows obtaining short turn-off time for a rather large lifetime close to collector p-n junction.

3.      Distributed amplifying gate: The distributed gate together with high values of lifetime close to collector p-n junction and in the p base provide fast turn-on of all of the thyristor area, reduced turn-on energy loss, and increased repetitive di/dt-rate and operating frequency.

 

Figure 1. Silicon elements of thyristors

 

Owing to the reduced Qrr and tq values, new thyristors can operate in the frequency band up to 30kHz for 1000…1500V blocking voltage range, up to 10kHz for 2200V blocking voltage range and of 2…5 kHz for 3400V blocking voltage range. The topology of thyristor element is adapted for high frequencies. New devices can reliably operate at repetitive di/dt’s of 800…1250 A/µs.

Symmetric Voltage Suppressors with Improved Power Capacity

 
Figure 2. Symmetric avalanche voltage suppressor with “conventional” structure and new device containing hidden n-layers with reduced specific resistance: 1 - Copper contact of the package, 2 – Contact metallization of semiconductor element, 3 – Filler,  4 – Semiconductor element, 5 – Molybdenum thermal compensator
 

 

For “conventional” structure devices, the problem area limiting peak values of dissipation power and avalanche current as well as maximum admissible energy loss is the periphery area adjacent to bevel. In this area, any polarity voltage applied increases current density, and heat dissipation is very poor because the upper contact size is smaller than the semiconductor element. New structure devices do not have such a problem: there is no avalanche current in the periphery area. This helps to increase peak avalanche current, peak dissipation power, and admissible energy loss.

Power High Voltage Impulse Diode-Thyristors

Power high-voltage impulse diode-thyristors can be produced on the basis of 4-layer thyristor elements with an integrated transistor element.

Figure 3. Integrated transistor element – voltage suppressor

A thyristor element is the main component of the device. A thyristor in this case plays the role of a high peak current switch. Avalanche current through the transistor element integrated into the three layer suppressor switches the thyristor element. If a thyristor has multiphase regeneration control, this element may be located within any of the amplifying areas or within all of them. Such a device can be used as a high power fast protective element or a current and voltage impulse switch.

 

For more information, please read:

Proton Irradiation Technology

 

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