ECEN 5843 - 2014 . Terahertz Transistors - Abhishek Divekar, Electrical and Computer Engineering, Oklahoma State University. Applications : Micro-controllers and micro-processors Medical imaging devices Grid computing systems Space research Astronomy devices and radio telescopes
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- Abhishek Divekar, Electrical and Computer Engineering, Oklahoma State University
In 2001, Intel, came up with a new transistor called as ‘Terahertz ‘ transistor that does not pose a challenge to Moore’s law; which allows doubling the number of transistors every two years. These transistors operate in GHz range and are 50 to 100 times faster than conventional transistors. They are highly efficient and consume less power. They solve the problems that are faced by conventional transistors.
Structure of Terahertz Transistor:
Terahertz transistors are FETs and not BJTs because FETs are faster, thermally more stable and less noisy than BJTs. These transistors are made from Indium Phosphide and Indium Gallium Arsenide which make them speedy and thermal handling efficient. They have thicker drain and source areas and there is an addition of very thin silicon layer below the drain and source regions which acts as an insulator.
Features of Terahertz Transistors:
These transistors are built in an extremely thin silicon substrate on top of insulation layer made up of oxide. The silicon layer is depleted
in order to create high drive current. The higher drive current leads to faster transistor ON-OFF switching. The thin oxide layer is added in order to reduce the leakage currents by hundred times, when the transistor is in OFF state.
High K Gate Dielectric:
A high K gate dielectric material is used in these transistors. This reduces gate leakage current and hence the power consumption to a great extent. Intel makes the claim that this design uses 0.6 volts for its operation.
No Sub-threshold Leakage:
The construction of this transistor is on a depleted silicon region on top of an oxide layer. This oxide layer acts as an insulator and separates the source, drain and the channel regions from the substrate. This layer prevents the current to pass through the substrate and hence does not provide path for the leakage current.
No Gate-oxide Leakage:
Terahertz transistors use a high K dielectric material made up of Zirconium dioxide (ZrO2). This gate dielectric material drastically reduces the gate leakage.
No Alpha Particle Effect:
The alpha particle effect is not seen in these transistors because of two reasons. Firstly, the substrate above the oxide layer is depleted of the charge carries so even if alpha particles strike this region, there wouldn’t be any charge build up. Secondly, if the alpha particles penetrate into the substrate region and if they cause the ionization of the charge carries, it would not matter much as the substrate is separated from the transistor by the oxide layer.
Terahertz transistors have large thickness of drain and source regions thus giving more area for the electrons to move and reducing the transistor resistance.
Low Operating Voltage:
Terahertz transistors operate at very low voltage which is approximately 0.6 volts. This is achieved because of low resistance and capacitance values, negligibly small sub-threshold leakage, gate-oxide leakage and alpha particle effect.