Metal diode enables terahertz transceiver
Metal diode enables terahertz transceiver
A new diode concept being developed at Phiar Corp. promises to enable terahertz detectors that could easily be integrated into silicon circuits, according to the company’s CEO and founder. Garrett Moddel described the technology at the recent Spring Meeting of the Materials Research Society in San Francisco.
Phiar has developed a full-RF system technology operating in the hundreds of gigahertz frequency range under the trade name Optenna.
Moddel demonstrated rectification of a 200GHz signal using his metal-insulator-insulator-metal (MIIM) diode. The novel structure creates a quantum well at the boundary between the two insulators that promotes extremely fast tunneling of electrons from one metal layer to the other. Moddel has recorded an electron transit time of one femtosecond, which is far shorter than the transit time across semiconductor interfaces.
The magic ingredient in the diode is the insulator material, which Moddel is not divulging because of patent proceedings. Initial research had produced a fast metal-insulator-metal diode, but this suffered from almost non-existent nonlinearity. The cure was to add a second insulator, which produced the quantum-well effect and a very strong nonlinearity at low power levels. The diode operates at the same voltage and power levels of semiconductor transistors.
By adding a third insulating layer and another metal layer, it is possible to turn the diode into a bipolar transistor structure. Another configuration elongates the metal layers into a two-lobed antenna. Each lobe is about a micron long, which is the wavelength of the incident radiation. Acting as a terahertz antenna, the surrounding metal generates surface plasmon waves in the insulator region that are able to filter the signal from the carrier.
Because the devices can be built with thin-film techniques, low-cost manufacturing that is compatible with existing semiconductor processing is possible. The thin-film process is also low-temperature, making it compatible with a variety of other substrates, such as plastic and glass. Moddel envisions integrating MIIM diodes and transistors as a post-process step in conventional silicon ICs.
Wideband communications are one set of applications that Phiar is targeting. Circuits using MIIM devices could directly drive wideband transmission at gigahertz frequencies. Further refinements are expected that could push it up into the emerging area of terahertz imaging.
The basic thin-film process can be used to create all the components for wireless transmission and detection.
An even larger application area is high-speed interconnect on PCBs. A terahertz transceiver circuit that can detect and transmit data at rates between 10Gbps and 100Gbps has been designed. The interconnect can be terahertz waveguides or free-space transmission over short distances.
The transceiver is built into the base of a socket that holds a packaged IC. Beneath the socket on the PCB is a diffraction grating that directs signals into and out of a waveguide built into the board. Two advantages of this design are the elimination of a physical connector, which can generate faults, and a relatively wide area for coupling the signal, which reduces alignment problems. The need for precise alignment has made optical interconnects expensive and difficult to implement.
Moddel, who is also a professor of electrical engineering at the University of Colorado, Boulder, founded Phiar in 2001 and has received backing from Menlo Ventures.
- Chappell Brown
EE Times