Over time transistors — the building blocks of electronic devices – are becoming smaller by the day, making apparatus quicker and compact. A group of Indian scientists have discovered a way to tackle this dilemma.
An example of this dual-gated apparatus developed by IISc Bengaluru scientists. Picture: India Science Wire
Transistors operate by acting like digital switches controlling the flow of current across circuits. The most common type of transistors known as MOSFETs (metal–oxide–semiconductor field-effect transistors) can’t switch from ‘on’ to ‘away’ unexpectedly and thus leak present even after the device is turned off. The smaller the transistors are somewhat more power they squander. Tunnel FETs (field-effect transistors) waste less power but are more appropriate for low-performance devices like watches or laptop computers.
Scientists at the Indian Institute of Science (IISc) in Bengaluru have combined these two different kinds of transistors into a single device that could easily switch between power-efficient and high-performance modes, depending on the requirement. The apparatus has a special type of metal-semiconductor junction which can be tweaked to make it act either like a MOSFET or even a tunnel FET.
When the gate is in the OFF position, there’s a large energy barrier which prevents electrons from crossing over. When the gate is switched on with voltage, the height of the barrier is decreased and electrons could jump over. The smaller the distribution voltage to turn the transistor on, more effective is the apparatus,” explained Dr. Navakanta Bhat, head of the Centre for Nano Science and Engineering at IISc who led the research group.
However, he said, bringing down supply voltage for MOSFETs proportionately with transistor size is tough due to a basic design flaw. A variable called subthreshold swing — that determines the minimal gate voltage required for the transistor to switch from on to off — limits the distribution voltage to be not less than one volt.
To overcome this, scientists have attempted utilizing tube FETs in which rather than their height, the diameter of the electron barrier is decreased to a stage where electrons are able to “tunnel” via instead of leaping over it. Tunnel FETs can operate at lower supply voltages however, also the current flowing when the transistor is on is significantly reduced.
In the present work, researchers made a hybrid device capable of switching between MOSFET and tube FET modes by using two gates instead of one, and a special type of electron barrier generated by joining a metallic and semiconductor under certain conditions. The dual-gated apparatus, Dr. Bhat said, can operate at a voltage lower than possible with standard MOSFETs, greatly reducing power consumption.
The research results are published in journal Applied Physics Letters. The team comprised Dr. Bhat and Shubhadeep Bhattacharjee.