A finished device: Optical microscope image of the transistor (left) and an ultra-scaled vertical nanowire (right). (Courtesy: Y Shao)
Topics: Electrical Engineering, Materials Science, Nanoengineering, Nanomaterials, Nanotechnology, Semiconductor Technology
A new transistor made from semiconducting vertical nanowires of gallium antimonide (GaSb) and indium arsenide (InAs) could rival today’s best silicon-based devices. The new transistors are switched on and off by electrons tunnelling through an energy barrier, making them highly energy-efficient. According to their developers at the Massachusetts Institute of Technology (MIT) in the US, they could be ideal for low-energy applications such as the Internet of Things (IoT).
Electronic transistors use an applied voltage to regulate the flow of electricity – that is, electrons – within a semiconductor chip. When this voltage is applied to a conventional silicon transistor, electrons climb over an energy barrier from one side of the device to the other, and it switches from an “off” state to an “on” one. This type of switching is the basis of modern information technology, but there is a fundamental physical limit on the threshold voltage required to get the electrons moving. This limit, which is sometimes termed the “Boltzmann tyranny” because it stems from the Boltzmann-like energy distribution of electrons in a semiconductor, puts a cap on the energy efficiency of this type of transistor.
Highly precise process
In the new work, MIT researchers led by electrical engineer Jesús A del Alamo made their transistor using a top-down fabrication technique they developed. This extremely precise process uses high-quality, epitaxially-grown structures and both dry and wet etching to fabricate nanowires just 6 nm in diameter. The researchers then placed a gate stack composed of a very thin gate dielectric and a metal gate on the sidewalls of the nanowires. Finally, they added point contacts to the source, gate and drain of the transistors using multiple planarization and etch-back steps.
Vertical-nanowire transistors defeat the Boltzmann tyranny, Isabelle Dumé, Physics World
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