High Linearity RF Transistors based on Carbon Nanotubes
The Linearity Problem
As mobile data applications proliferate, the demands for system and device level performance puts extraordinary performance pressure on the Radio Frequency (RF) front-end components to deliver higher data rates at the same or lower power levels. The key to solving these obstacles lies in improving the linearity of analog RF components.
It can be argued that we are reaching the Shannon limit for communications and improvements based purely on digital modulation techniques such as MIMO and further channel coding will provide incremental benefits at best. In addition, these advanced techniques have a detrimental effect on power consumption and even the most up to date 4G devices operate at very low efficiencies when delivering the highest data rates, particularly at full transmit power, and ultimately consuming a great deal of excess power in the process.
To permit higher data rates and channel capacity at lower power levels will require an innovation in analog components. In particular, increased linearity in all front end components – specifically amplifiers (PA, LNA and mixers) – will reduce noise, interference and distortion while also reducing power consumption, and by increasing the available signal to noise ratio, will open the door to further innovations in digital processing.
Through vastly improved linearity these advanced RF components will support further coding advances in the digital domain and generate less out-of-band interference (and intermodulation), further enhancing spectral efficiency and providing More Data for Less Power. We believe that CFETS represent that innovation.
CFETS Address the Linearity Constraint
Over the past 20 years, research on carbon nanotubes (CNTs) has demonstrated material properties that are orders of magnitude better than bulk semiconductors such as Silicon and GaAs. Due to their intrinsic performance, a mere 1% CNT packing fraction could enable power densities equivalent to GaAs and access to CNT properties – from low noise to intrinsic linearity and temperature robustness, making them ideally suited for mobile applications.
Inherently linear, CNT based Field Effect Transistors (CFETs) are highly efficient, dissipating less unwanted power than current state of the art technology while handling high power levels. This translates into more battery life for mobile devices with lower associated cooling costs. Looking forward, CFETs based architectures can reshape the world of analog RF electronics, enabling the higher data rates and improved capacity demanded by next generation wireless systems due to their intrinsic linearity and associated low out-of-band interference.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure with one or more layers of graphene (lattice). Diameters of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are typically 0.8 to 2 nm and 5 to 20 nm, respectively, although MWNT diameters can exceed 100 nm. CNT lengths range from less than 100 nm to 0.5 m and Nanotubes with length-to-diameter ratio of up to 132,000,000:1 have been constructed, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. Because of its nanoscale cross-section, electrons propagate only along the tube's axis. As a result, carbon nanotubes are frequently referred to as one-dimensional conductors. Since the electron mean free path in SWCNTs can be as long as 1 micrometer, long channel CNTFETs exhibit near-ballistic transport characteristics, resulting in high speeds and intrinsically linear operation.
Carbon Technology Inc. is developing technology and processes to fully harness the disruptive RF performance that CFETs can deliver. Carbon electronics has become one of the fastest growing and best funded areas of global research and development, with Carbon Technology Inc standing at the forefront of this movement, with enabling technology applied to solving the critical problem of spectral efficiency and the associated power dissipation generated by an exponentially growing demand for mobile data.