Tuesday, July 22, 2014

Current and Future Transistor Technology

In the age of CMOS, we have developed different transistor technologies to make device smarter, faster and operate in any condition. Research in VLSI has taken future steps for the upcoming generation. SiliconMentor is a platform for the VLSI engineers to utilize their technical skills for the creation and development of a device that can be operated at several parameters.
A few of the present and future transistor technologies are described below:


*UTB SOI *CNT FET *SET *Vacuum channel Transistor

*Tunnel FET *SiNW FET *Plasma Transistor *Green FET

*Graphene based 2-D transistor *Spin-MOSFET *optical transistor

Ultra thin Body Silicon-on-Insulator: Its name suggests that a silicon layer or MOS develops on the insulating layer. It can eliminate the punchthrough path between drain and source. It also removes the short-channel effects. Many companies work at UTB-SOI transistor technology.
FinFET:  In FinFET, the conducting channel is enfolded by a thin silicon "fin", which forms the body of the transistor. The thickness of the fin (measured in the direction from source to drain) determines the effective channel length of the device. The enfold-around gate structure provides a better electrical control over the channel and thus helps in reducing the leakage current and overcoming other short channel effects.
Vacuum Channel Transistor: In this new transistor, electrons propagate freely through the nothingness of a vacuum and it produces less noise and distortion than solid state semiconductor materials. Vacuum-channel transistors could work 10 times as fast as ordinary silicon transistors and may be able to operate at terahertz frequencies, which is beyond the reach of any solid-state device. 
CNT FET: CNT FET uses carbon nanotube as the channel instead of bulk.  CNT transistor switches using less power than ordinary silicon bulk transistor. It has better compatibility with high-k dielectric and five times higher transconductance.
Tunnel FET: A new transistor design—the tunnel FET or TFET (we take the advantage of tunnelling of electrons through thin barriers in MOSFET) which works by raising or lowering an energy barrier to control the flow of current, the tunnel transistor keeps this energy barrier high. The device switches on and off by changing the probability that electrons on one side of that barrier will materialize on the other side. In the tunnel FET, we use the gate to control the electrical thickness of the barrier and thus the probability that electrons can slip through it.
In a TFET, we use p-i-n and n-i-p configurations for transistor. The intrinsic state (electron as well as holes) corresponds to the maximum resistivity that a semiconductor can have. TFETs should be able to switch with a much smaller voltage swing than that required in a MOSFET. Tunnel junctions like the one used in the TFET are also widely used to connect multijunction solar cells and to trigger semiconductor-based quantum cascade lasers.
Single electron transistor: Two electrodes (drain and source) connected through tunnel junctions to one common electrode with a low self-capacitance, known as the island (or Quantum Dot). The electrical potential of the island can be tuned by a third electrode (known as the gate) which is capacitively coupled to the island.
Transistor that runs on Protons: Scientists have developed a first solid-state transistor that controls the flow of protons instead of electrons. The device could help to interface at a molecular level with living systems, since biology commonly involves protons and ions to perform work and transmit information. There are no p-n junctions to block current when the device is off. So the device functions more like a wire with variable conductivity than as a perfect switch. 
In this transistor, palladium was the key to getting the transistor to work, because it is one of a rare group of materials that can absorb hydrogen, creating a hydride that can easily accept and donate protons. Using this material to build the source and the drain allowed the team to inject protons into the channel just as in an electronic transistor.
Plasma transistor: The new micro-plasma transistors work at temperatures of up to 790 °C (inside nuclear reactors). They could be used to make electronics for controlling robots that conduct tasks inside a nuclear reactor. The channel in a plasma transistor consists of a partially ionized gas, or plasma, instead of a semiconductor bulk. An electron emitter (typically silicon) injects electrons into the plasma when a voltage is applied to it. Plasmas are generated at high temperatures, making them suitable for a risky-environment transistor. In addition to working in nuclear reactors, the new high degree-temperature transistors could be used to generate X-rays.
Optical transistor:
An optical transistor is a device that amplifies or switches optical signals. Light fall on an optical transistor’s input changes the intensity of light emitted from the transistor’s output. Since the input signal intensity may be weaker than that of the source, this transistor amplifies the optical signal. Optical transistors provide a means to control light using only light and has applications in optical computing and fiber-optic communication networks.
Grephene based Transistor:
Graphene is a 2-D one atom thick layer of graphite. It is light, strong, nearly transparent and excellent conductor of heat and electricity.
A transparent thin-film transistor (TFT) has developed from tungsten diselenide (WSe2)/ molybdenum disulfide (MoS2) as the semiconducting layer, graphene for the electrodes and hexagonal boron nitride as the insulator.

                                                   Author - Deepak Berwal
                                            (Research Associate at Silicon Mentor)
Future Transistor technology : VLSI