The IGBT Device

Physics, Design and Applications of the Insulated Gate Bipolar Transistor

B. Jayant Baliga

• Publisher: William Andrew
• Year: 2015
• ISBN:
  9781455731534
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The IGBT device has proved to be a highly important Power Semiconductor, providing the basis for adjustable speed motor drives (used in air conditioning and refrigeration and railway locomotives), electronic ignition systems for gasolinepowered motor vehicles and energy-saving compact fluorescent light bulbs. Recent applications include plasma displays (flat-screen TVs) and electric power transmission systems, alternative energy systems and energy storage. This book is the first available to cover the applications of the IGBT, and provide the essential information needed by applications engineers to design new products using the device, in sectors including consumer, industrial, lighting, transportation, medical and renewable energy.

The author, B. Jayant Baliga, invented the IGBT in 1980 while working for GE. His book will unlock IGBT for a new generation of engineering applications, making it essential reading for a wide audience of electrical engineers and design engineers, as well as an important publication for semiconductor specialists.

• Essential design information for applications engineers utilizing IGBTs in the consumer, industrial, lighting, transportation, medical and renewable energy sectors.
• Readers will learn the methodology for the design of IGBT chips including edge terminations, cell topologies, gate layouts, and integrated current sensors.
• The first book to cover applications of the IGBT, a device manufactured around the world by more than a dozen companies with sales exceeding $5 Billion; written by the inventor of the device.

Chapter 1

Introduction

Abstract

The pervasive use of the insulated-gate bipolar transistor (IGBT) in all sectors of the economy has made it an essential element for improving the comfort, convenience, and quality of life for billions of people around the world. After a discussion of the applications spectrum for power devices, this chapter describes the basic structure and operating principle of the IGBT. The circumstances and efforts undertaken to take the device from concept to a commercialized product are described to provide a historical perspective. The rapid growth in power ratings for the IGBT is traced over the last 30 years.

Keywords

Applications spectrum; Asymmetric; Commercialization history; IGBT structure; Ratings growth; Symmetric

Today, the insulated-gate bipolar transistor (IGBT) is pervasively used in power electronic systems and their applications to improve the comfort and quality of life for billions of people from around the world. The impact of the IGBT on society can be measured by asking the question: “What would happen if IGBTs were removed from all of the applications that they serve today?” The answer is quite revealing:

1. Our gasoline powered cars would stop running because the electronic ignition systems would no longer function;

2. Our hybrid electric and electric cars would stop running because the inverters used to deliver power from the batteries to the motors would no longer function;

3. Our electric mass transit systems would come to a standstill because the inverters used to deliver power from the electric grid to the motors would no longer function;

4. Our air-conditioning systems in homes and offices would stop working because the inverters used to deliver power from the utility company to the heat pumps and compressors would no longer function;

5. Our refrigerators and vending machines would no longer function making the delivery and storage of perishable products impossible;

6. Our factories would come to a grinding halt because the controllers used to run the robots would cease to function;

7. Our new low-energy compact fluorescent bulbs would stop functioning significantly increasing power consumption for lighting due to reverting back to incandescent bulbs;

8. Our portable defibrillators recently deployed in emergency vehicles, on-board airplanes, and in office buildings would no longer be operational putting over 100,000 people at the risk of death from cardiac failure every year;

9. Our new solar- and wind-based renewable energy sources would not be able to deliver power to the grid because the inverters would stop functioning;

10. Our uninterruptible power supplies would no longer work jeopardizing financial transactions conducted by banks and investment firms;

11. The flash in modern cell phones and digital cameras would be inoperable ruining the documentation of many memorable moments in our lives.

In conclusion, the quality of life in our society would be greatly impaired if the IGBT is no longer available. In other words, the IGBT has become an embedded technology that enriches the lives of billions of people from around the globe by providing comfort in the home, food preservation, industrial manufacturing, transportation, and even medical assistance.

In September 2005, when celebrating their 30th anniversary of covering trends in power semiconductor technology, Power Electronics Technology magazine published a review article [1] with a milestone chart. In their milestone chart, the first significant event highlighted is the invention of the bipolar transistor by Brattain, Bardeen, and Shockley in 1947 for which they received the Nobel Prize in 1956. The next important milestone is the invention of the integrated circuit by Jack Kilby, who received a Nobel Prize in 2000. The conception of the integrated circuit is also credited to Robert Noyce, who received the National Medal of Technology and Innovation in 1987. During the 1950s, power thyristors were also commercially introduced for high-power applications. Major manufacturers for these bipolar devices were General Electric and Westinghouse Corporation. According to the milestone chart, the next major innovation in power devices was the introduction of the power MOSFETs by Siliconix in 1975 and International Rectifier in 1978. At this time, the power semiconductor industry was bifurcated into two tracks with one group of companies producing bipolar power devices and a separate group of companies producing power MOSFET devices. At that time, the manufacturing of these devices was considered to be incompatible because the MOS devices required know-how in control of semiconductor surface properties, while the bipolar devices relied up on control of minority carriers within the bulk regions of semiconductors.

The milestone chart states that I invented the IGBT in 1979–1980. This was accomplished by proposing the functional integration of MOS and bipolar physics within the same monolithic structure. In December 2010, I was inducted into the Electronic Design Engineering Hall of Fame for the invention, development, and commercialization of the IGBT. The award announcement states [2]: “While working at General Electric in the late 1970s, Baliga conceived the idea of a functional integration of MOS technology and bipolar physics that directly led to the IGBT's development … it remains undeniable that Baliga's vision and leadership played a critical role in moving the IGBT from a paper-based concept to a viable product with many practical applications.” On October 21, 2011, President Obama presented the National Medal of Technology and Innovation to me at the White House in recognition for my development and commercialization of the IGBT and other power semiconductor devices. This recognition put the spot light on IGBTs and acknowledged the impact of power electronics on our society.

1.1. IGBT Applications Spectrum

IGBTs are required for applications that operate over a broad spectrum of current and voltage levels as shown in Fig. 1.1. Their characteristics are ideal for applications with operating voltages above 200 V. Typical examples are lamp ballasts, consumer appliances that utilize motors, and electric vehicle drives. Other examples are high-power motor control in steel mills and for traction (electric trains). They are now being utilized even in power transmission and distribution systems. The on-resistance of conventional silicon power MOSFET structures is too large to serve these applications. Consequently, these applications utilize silicon IGBTs today. Silicon carbide (SiC) IGBTs offer very promising characteristics for applications that require blocking voltages of above 10–15 kV for use in smart grid applications [3].

Figure 1.1 Application spectrum for insulated-gate bipolar transistors (IGBTs).

It is worth pointing out that the current ratings for the IGBTs increase with increasing voltage rating for these applications with the exception of the smart grid. In the case of silicon IGBTs, this issue is tackled by resorting to multichip press-pack modules. The smart grid application is unique in requiring very high voltage devices with low current ratings. These applications can be served by using SiC-based IGBTs despite the lower chip manufacturing yield and higher cost of SiC wafers. These SiC IGBTs can operate at higher frequencies than their silicon counterparts resulting in a smaller size for the magnetic elements used in the power circuits.

1.2. Basic IGBT Device Structures

As illustrated in Fig. 1.2, there two basic IGBT structures, namely the symmetric blocking and the asymmetric blocking devices. The symmetric blocking structure allows supporting a high voltage in the first and third quadrant, i.e., the device has high forward and reverse blocking capability. This feature is required for any power devices used in high-voltage AC power applications. In contrast, the asymmetric blocking structure can support a high voltage only in the forward blocking mode. This structure is optimized for applications that utilize a high-voltage DC power bus. The presence of the N-buffer layer in the asymmetric structure allows reducing the thickness of the N-drift region which improves the on-state voltage drop and switching time.

Figure 1.2 Basic insulated-gate bipolar transistor device structures.

1.3. IGBT Development and Commercialization History

The first semiconductor power devices were bipolar transistors that evolved out of the invention of the junction transistor in 1947. A thick, lightly doped drift region was added in the power bipolar transistor as illustrated in Fig. 1.3 in order to support high voltages. The high blocking voltage capability also required a relatively large base width that degraded the current gain. High-level injection effects produced further reduction of the current gain [4]. The large base drive current required for the bipolar transistor restricted its voltage rating to below 600 V.

High-power applications that needed devices capable of supporting more than 1000 V and controlling large currents were served in the 1970s by the development of thyristor or four-layer semiconductor structures. The gate turnoff thyristor (GTO) shown in Fig. 1.3 became popular for motor drives in traction applications for street cars and electric trains. The thyristor regenerative action within these four-layer switches allowed manufacturing high current devices with low on-state voltage drop. However, the GTO required very large gate drive currents to achieve unity gain turnoff. The complex gate drive and snubber circuits for GTOs increased power losses, and added cost and size to the system.

Figure 1.3 Bipolar power devices.

During the 1970s, a concerted effort was made to create power MOSFETs after the successful development of Complementary Metal Oxide Semiconductor (CMOS) technology. The double-diffused or DMOS structure shown in Fi...