Junctionless Field-Effect Transistors
Junctionless Field-Effect Transistors: Design, Modeling, and Simulation is an essential resource for CMOS device design researchers and advanced students in the field of physics and semiconductor devices. SHUBHAM SAHAY, P H D, is a Post-Doctoral Research Scholar in the Department of Electrical and Computer Engineering, University of California, Santa Barbara. He has authored several peer-reviewed journal articles on topics including semiconductor device design and modeling and unconventional applications of emerging non-volatile memories. MAMIDALA JAGADESH KUMAR, P H D, is a Professor at the Indian Institute of Technology, New Delhi and Vice-Chancellor of Jawaharlal Nehru University, New Delhi. He is Editor-in-Chief of IETE Technical Review and has widely published in the area of Micro/Nanoelectronics.
Junctionless Field-Effect Transistors
Introduction to Field-Effect Transistors
We are living in an era of information technology where smartphones, smart watches, and smart technology have become an inevitable part of our lives. You might have observed a drastic improvement in the performance of these smart devices. For instance, the shift from single core processors to multicore processors, the increase in CPU's frequency from few MHz to several GHz, the increase in the RAM from few MB to several GB, and so on. All these factors have led to a tremendous increase in the performance of these computing devices. The smart devices found in every household nowadays have a performance metric comparable to the earlier supercomputers. For instance, the Apple watch has twice the processing power of a 1985 Cray-2 supercomputer . In addition, the device size has also shrunk significantly and the focus in the research and development of computing devices has shifted toward mobile devices. Moreover, the functionality per device has also increased considerably. For instance, the present day smartphones not only have processing capabilities of a supercomputer but can also perform the functions of a good quality camera, a Wi-Fi dongle, an X-BOX gaming system, and so on. To summarize, every other person in this modern era has access to low-cost, high-performance gadgets.
Have you ever wondered what drives the "smartness" and the supercomputing capabilities of all the smart technology gadgets? Let us try to understand this from a human body-gadget analogy. Just like the human body is composed of cells as the building block, the electronic gadgets are made up of transistors. In human body, the cells are grouped together to perform a particular function and form an organ. Therefore, the efficiency and the number of different functions that can be performed by the body depends exclusively on these cells. Similarly, the transistors act like a switch and are wired together in a chip (which is similar to the organ from body-gadget analogy) in a specific manner to enable a particular function. The larger the number of transistors in a gadget, the more the number of functions it can perform. The research and development in the field of transistors has driven this "smart" revolution. It is indeed very interesting how such small chunks of silicon chips drive our lives.
1.1 Transistor Action
But what exactly is a transistor? The word transistor was given by its first inventors: Shockley, Brattain, and Bardeen in 1947 [2-5]. At that time, no one would have wondered that this discovery (which actually was an accident) would be driving the lives of common people for generations to come. The transistors are often conceived as a device where the resistance between two terminals may be controlled by the current/voltage at the third terminal. Therefore, transistor refers to any three-terminal device where the current (or voltage) between two terminals may be controlled by the action of voltage (or current) at the third terminal.
In the subsequent sections, we shall see how the most common transistors work from both a qualitative approach and an energy band diagram perspective. The bipolar junction transistors (BJTs) dominated the semiconductor industry until late 1970s. Although BJTs are still used in the high-frequency circuits such as in radio frequency circuits, the throne is captured by the metal-oxide-semiconductor field-effect transistors (MOSFETs) and they continue to drive the semiconductor industry even today. Therefore, we shall discuss the MOSFETs in detail in the next section.
Transistors such as MOSFETs act as switches in the integrated circuits. However, it may be noted that the MOSFETs are not ideal switches (which are expected to consume no power when switched-OFF and deliver a high current instantaneously when switched-ON). The MOSFETs exhibit a small leakage current and, therefore, con