mm-Wave Radar Circuits
Lars Ohlson, Lars-Erik Wernersson
We use the novel opportunities provided by optimized nanoelectronic device architectures to achieve avant-garde implementations for millimetre-wave (mmW), 30-300 GHz, radar systems. The work is performed in cross-disciplinary collaborations that combine process integration and device innovations in integrated circuit technology as well as system verification by applied measurements and signal processing schemes.
Imaging, tracking, and material spectroscopy are just a few of the attractive possibilities provided by radar technology. A wideband electromagnetic pulse provides spatial resolution while its carrier frequency sets the material contrast or penetration properties. Implementation of a radar system requires everything from a high-power transmitter, wideband antennas, and a sensitive receiver as well as everything in between and around these components. Transceiver technologies aiming at wideband pulses and low-power operation are targeted.
We have developed unique high frequency pulse generators, operating in the mmW spectrum . The technology is based on resonant tunnel diodes (RTDs), which have wideband negative differential conductance due to physical quantum effects. Implemented in an oscillator circuit, these diodes provide competitive output power levels. High-speed III-V surface-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are used to switch the mmW oscillator core on and off, creating picosecond-short wideband pulses . Radar front-end building blocks can also be implemented in our various III-V surface-channel and nanowire MOSFET technologies.
Wideband and non-dispersive leaky-lens antennas are ideal for transmission of the wideband pulses , but compact co-designed dielectric resonator antennas (DRAs) have also proved useful for on-chip monolithic integration . Initial studies on material spectroscopy have demonstrated wideband identification of material parameters by free-space measurement techniques . Further studies on multi-layer structures and organic materials are attractive for demonstration of non-destructive testing and medical imaging techniques.
M. Egard, M. Ärlelid, L. Ohlsson, B. M. Borg, E. Lind, and L.-E. Wernersson, “In0.53Ga0.47As RTD-MOSFET Millimeter-Wave Wavelet Generator,” IEEE Electron Device Lett., vol. 33, no. 7, pp. 970–972, Jul. 2012.
L. Ohlsson, P. Fay, and L.-E. Wernersson, “Picosecond Dynamics in a Millimetre-Wave RTD-MOSFET Wavelet Generator,” IET Electron. Lett., vol. 51, no. 21, pp. 1671–1673, Oct. 2015.
I. Vakili, L. Ohlsson, M. Gustafsson, and L.-E. Wernersson, “Wideband and Non-Dispersive Wavelet Transmission Using Leaky Lens Antenna,” IET Electron. Lett., vol. 49, no. 5, pp. 321–322, Feb. 2013
Ohlsson+etal2014: L. Ohlsson, T. Bryllert, D. Sjöberg, and L.-E. Wernersson, “Monolithically-Integrated Millimetre-Wave Wavelet Transmitter With On-Chip Antenna,” IEEE Microw. Wireless Compon. Lett., vol. 24, no. 9, pp. 625–627, Sep. 2014.
I. Vakili, L. Ohlsson, L.-E. Wernersson, M. Gustafsson, “Time-Domain System for Millimeter-Wave Material Characterization,” IEEE Trans. Microw. Theory Techn., vol. 63, no. 9, pp. 2915–2922, Sept. 2015.
Lateral Nanowire THz MOSFETs
We develop and study the physics and applications of very high performance lateral III-V nanowire MOSFETs. These devices are highly scaled, and of importance for VLSI and RF applications. At highly scaled gate lengths (Lg<20 nm) with the appropriate technology, active THz device operation can potentially be achieved. The highly scaled nanowires are operating in the few sub band limit, demonstrating quantized conductance. We perform advanced process development and transistor scaling to improve the device performance. Quantum mechanical device models are being developed for improved understanding of the DC, RF and noise properties for 1D FETs. The circuit applications of 1D devices are further considered.
Vertical Nanowire MOSFETs
Arrays of vertical nanowires are attractive for MOSFETs due to the possibility of integration of materials with large lattice mismatch, a gate-all-around geometry and a small device footprint area. We are developing III-V MOSFETs for both analog and low-power digital applications using InAs, InGaAs and GaSb nanowires. We are developing novel growth and processing techniques to enable e.g. cointegration of n- and p-type III-V materials on Si, selfaligned gates, CV characterization and implementation of demonstrator circuits.
Steep Slope Transistors
Erik Lind, Lars-Erik Wernersson
In a traditional MOSFET, which relies on thermionic emission of carriers over a potential barrier, there is a fundamental limit to how efficient the current is modulated by the gate voltage. In contrast a TFET exploits quantum mechanical band-to-band tunneling as an energy filter enabling a much steeper characteristic allowing operation at very low voltages. We are using arrays of vertical InAs/GaSb nanowires on Si to achieve high current densities due to the broken band gap alignment and good electrostatics due to the gate-all-around geometry. RF, noise and temperature dependent electrical characterization is used to gain further understanding about the transport and optimize the devices for various low-power applications.
Photodetectors operating in the long wavelength infrared region (LWIR) are important for applications in e.g. thermal imaging, astronomy and gas detection. InAsSb has a band gap which can be tuned by its composition enabling detection up to around 10 µm but the lack of a lattice matched substrate material prevents planar growth with high crystal quality. We are growing InAs/InAsSb nanowires on Si substrates which circumvents the lattice mismatch problem. The nanowire geometry leads to diameter dependent resonant absorption that efficently couples light into the wires at specific wavelengths making our approach highly attractive for low noise IR detectors.