A New Multimodal Architecture Said to Redefine the Way Transistors WorkNovember 02, 2020 by Jake Hertz
Researchers at the University of Surrey have come up with a new type of transistor that offers linear behavior and huge upside.
Traditional MOSFET transistors are the fundamental building block of almost all modern electronics, yet they are far from perfect devices. For starters, they’re non-linear devices, complicating designs and analysis. Furthermore, in these transistors, the device’s digital and analog operations are both controlled by an applied voltage at a gate electrode.
In a digital sense, the voltage is used to turn the transistor on or off. In an analog sense, the gate voltage, more specifically the gate-to-source voltage, sets a number of characteristics such as transconductance and gain.
The Multimodal Transistor
Inspired to remove the non-idealities of the MOSFET transistor, researchers at the University of Surrey have designed a new type of transistor. The new transistor, dubbed the multimodal transistor (MMT), has an innovative layout that offers some huge upside potential.
In its basic structure, the MMT consists of four terminals (not including the body): a source, drain, and two control gates (CG1 and CG2). Like a conventional MOSFET, the source and drain are separated by semiconductor material while the control gates are separated by insulating layers.
Sitting above the source, CG1 provides the means for controlling the quantity of charge injected into the device (i.e the amount of current). The channel control gate, CG2 sits above the source-drain gap and toggles the conduction state of the semiconductor between the source and drain.
MMT layout. Screenshot used courtesy of the University of Surrey
The unique aspect of this architecture is that CG1 exclusively controls the current level, whereas CG2 exclusively controls the on/off state of the device without affecting the magnitude of current flow. This combined analog injection and digital switching make the device exceptionally versatile.
Three Configurations of the Multimodal Transistor
Shown below are three test cases that demonstrate the functionality of this device in a common-source configuration.
Three test cases of the MMT. Screenshot used courtesy of the University of Surrey
Looking from left to right, the first example shows a positive voltage applied to CG2 and ground applied to CG1. Here, the conducting channel between drain and source is turned on by the voltage at CG2. But even though there is a large VDS, current will not flow in the absence of a positive CG1 voltage.
In the next example, a positive voltage is applied to CG1 and ground is applied to CG2. Grounding CG2 effectively turns off the conduction channel, so no current will flow through the channel.
Finally, the third example shows where both CG1 and CG2 have a positive voltage applied. In this example, the current will flow across the channel. The magnitude of that current is set explicitly by the voltage on CG1 and nothing else.
A Transistor as a Linear Device
This research, which is published in Advanced Intelligent Systems, is important because the MMT represents a transistor that is a linear device. This means that there is a linear dependence between output and input. This capability affords engineers with unprecedented freedom of design and could likely lead to simpler designs requiring less analysis and fewer transistors—and fewer transistors means less area and a higher yield rate.
The researchers also claim this device offers a tenfold increase in switching speed and tolerance to process variations. In addition, the analog/digital versatility of the MMT introduces new opportunities for thin-film technologies, including compact circuits for integrated processing at the edge and energy-efficient analog computation.