Schematic of a vertical tunnel field effect transistor. Images: Datta Lab, Penn StatePenn State Univ. researchers have proved the feasibility of a new type of transistor that could make possible fast and low-power computing devices for energy constrained applications such as smart sensor networks, implantable medical electronics, and ultra-mobile computing. Called a near broken-gap tunnel field effect transistor (TFET), the new device uses the quantum mechanical tunneling of electrons through an ultrathin energy barrier to provide high current at low voltage.

Penn State, the National Institute of Standards and Technology (NIST), and IQE, a specialty wafer manufacturer, jointly presented their findings at the International Electron Devices Meeting held in Washington, D.C., Dec. 9-11. The IEDM meeting is attended by a global audience that includes representatives from all of the major chip companies and is the prestigious forum for reporting breakthroughs in semiconductor and electronic technologies.

Tunnel field effect transistors are considered to be a potential replacement for current CMOS transistors, as device makers search for a way to continue shrinking the size of transistors and packing more transistors into a given area, often referred to as Moore’s Law. The main challenge facing current chip technology is that as size decreases, the power required to operate transistors does not decrease in step. The results can be seen in batteries that drain faster and increasing heat dissipation that can damage delicate electronic circuits. Various new types of transistor architecture using materials other than the standard silicon are being studied to overcome the power consumption challenge.

Transmission electron microscope cross section of the vertical TFET. The interface of the source and channel is the point where electron tunneling occurs. ILD is the interlayer dielectric separating the contacts. Top plane contacts are Gold (Au), Palladium (Pd), and Molybdenum (Mo).“This transistor has previously been developed in our lab to replace MOSFET transistors for logic applications and to address power issues,” said lead author and Penn State graduate student Bijesh Rajamohanan. “In this work we went a step beyond and showed the capability of operating at high frequency, which is handy for applications where power concerns are critical, such as processing and transmitting information from devices implanted inside the human body.” For implanted devices, generating too much power and heat can damage the tissue that is being monitored, while draining the battery requires frequent replacement surgery. The researchers, led by Penn State professor of electrical engineering, Suman Datta, tuned the material composition of the indium gallium arsenide/gallium arsenide antimony so that the energy barrier was close to zero (or near broken gap), which allowed electrons to tunnel through the barrier when desired. To improve amplification, the researchers moved all the contacts to the same plane at the top surface of the vertical transistor.

This device was developed as part of a larger program sponsored by the National Science Foundation through the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (NERC-ASSIST). The broader goal of the ASSIST program is to develop battery-free, body-powered wearable health monitoring systems with Penn State University, North Carolina State University, University of Virginia, and Florida International University as participating institutions.

Technical specifications

A scanning electron microscope top view of the TFET.The paper, "Demonstration of InGaAs/GaAsSb Near Broken-gap Tunnel FET with Ion=740µA/µm, GM=700µS/µm and Gigahertz Switching Performance at VDS=0.5V" reports on research leading to the demonstration of near broken-gap tunnel field effect transistors (NBTFETs) with a 200nm channel length that exhibited record drive current (ION) of 740µA/µm, intrinsic RF transconductance (GM) of 700µS/µm and a cut-off frequency (FT) of 19GHz at a source-drain voltage (VDS) of 0.5V. The work demonstrates the potential use of InGaAs/GaAsSb based TFET device technology to produce high performance devices that operate at very low voltages, offering simultaneously the low power consumption and high efficiencies needed for a wide range of power constrained applications. The work was supported under the ASSIST Award Number EEC- 1160483.

This paper will be available in the conference proceedings publication of the IEDM, the premier electron device conference. For further information, contact Suman Datta at or Bijesh Rajamohanan

Source: Penn State Univ.