RFIC Development: On-Chip Research

Principal Faculty Investigators: Ted Rappaport, Arjang Hassibi
Student Researchers: Craig Christianson
Principal Research Associate: Lawrence Ragan

This work was sponsored by the Army Research Office, Project W911NF-05-2-0044, and by the Advanced Microelectronics Research Center of The University of Texas at Austin.

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Current Research:

On-chip Antennas Using Frequency Selective Surface (FSS)
Efficient Laptop Antenna Array
Embedded On-chip Antennas and Signal Processing for Futuristic ICs, Including Adaptive and Lossy Structures

On-chip Antennas Using Frequency Selective Surface (FSS)

Utilizing only the metal interconnect layers of a high speed integrated circuit process, a proposed structure is expected to result in efficient on-chip antennas and arrays for radio frequency integrated Systems On Chip (SOCs).
If the shield plane of a semiconductor is patterned with holes to create a mesh, a Frequently Selective Surface (FSS) is produced and can be arranged to provide high wave impedance over a narrow band around the operating frequency. This results in a reflection of the wave from the antenna toward the semiconductor chip in phase with the wave propagating away from the chip.
Energy is radiated in the half space away from the top surface of the chip where the antenna lies, adding to the energy normally radiated in this direction. This prevents losses in the semiconductor and reduces them substantially in the shield plane, as induced currents are minimized.
There are various geometries of mesh structures and techniques for designing them that are applicable to the on-chip antenna with FSS configuration. Variable capacitors could be realized with structures in the silicon, such as varactor diodes or MOS capacitors, which can be voltage tuned.
It may be possible, through careful design, to allow limited interconnect of semiconductor circuits through the FSS, and the FSS could serve as a power or ground plane for other circuitry on the chip.
Multiple metal layers can be used to realize thick FSS structures, for example a resonant "coil" which would have multiple turns, or a "thick coil" which would be realized on multiple layers parallel connected by vias. One could also utilize multi-layer capacitors in resonant structures for FSS using this technique.
An "Active FSS" can also exist, where each resonant node of the FSS is enhanced with an on-chip amplifier to compensate for losses in metal and/or variable capacitors, if used.
After further research and development of design techniques, the projected results are much lower cost communications and radar systems in the mm wave portion of the radio frequency spectrum.

Efficient Laptop Antenna Array

Developed method of inexpensive design for utilizing combination of PWB antennas and PWB FSS in a laptop lid to facilitate one-sided, efficient, easily matched antennas for Multiple Input Multiple Output (MIMO) antennas and/or steerable arrays, with advantages in coverage and data throughput to wireless networks.
Use of FSS allows for an antenna to be placed in close proximity to a "ground" or "power supply" plane of a printed wiring board with enhanced efficiency of antennas in difficult environment of laptop lid, negating harmful effects of LCD structure.
FSS structures are inherently narrow band, so providing the necessary bandwidth in the FSS design could become a challenge.
Applications include enhanced laptop service from wireless networks, offering better range, coverage, and/or data throughput. In the future, the design could be used in any structure to facilitate efficient antennas in the presence of LCD displays.

Embedded On-chip Antennas and Signal Processing for Futuristic ICs, Including Adaptive and Lossy Structures

Frequency Selective Surface (FSS) reflects in phase/out of phase with metal sheet behind it. Application is laptop with FSS on the screen. Picture a FSS with lossy dielectric between it and metal. Have different reflectance/reflective at different frequencies. Receiver could be much easier than Transmitter.
If FSS is passive on a chip, you can switch really fast because of close proximity of leads and device. Super low power since switching doesn't take much power at all.
On-chip FSS could be used as RF filter, attenuate a loud interfering signal in nearby band, by using FSS and exploiting its tunabilty as part of an antenna or at high frequency mixer. Use FSS at the antenna to do RF tuning as part of the antenna circuit, which would make 60 GHz and higher frequency devices "tunable" with "filtering" in a cheaper way than conventional down conversion and filtering.
Use multiple layers of FSS stacked above each other to make different frequencies invisible or visible.
Put FSS structures (either single or multi-layers on skin of a surface (say an airplane or cell phone) where the FSS can reflect certain frequencies (such as radar or unwanted signals), and that the FSS can be switched to different frequencies through switching of FSS elements.
On-Chip - control an active angle, detect or sense if RF is there (very low power). Can do on-chip or off-chip, depends on physically the area you have to work with, but we can sense RF coming from different angles with FSS.
FSS Array - active in the sense that radiation is detected and then we (the FSS device, the chip, the radio, etc.) take some action - reflect, absorb, attenuate, control an antenna steering, or a reconfiguration of the FSS, based on what radiations was sensed.
Switch at antenna/FSS, on-chip to do down conversion and filtering all at once -- tunable by FSS and switching.
RFID, remove baseband protocol and now do switching on/off with FSS for synch/identification/communication in close proximity - very low battery drain and enough frequency selectivity/sensitivity to allow it to work in crowded spectrum. Possible applications in key fobs for cars, RFID handshake in grocery stores, etc.
Harvest power by tuning FSS to grab in-air power at specific "loud" frequencies, and then collect and store that received signal power. FSS will create a tuned/resonant circuit or will change an antenna pattern in order to adjust the device to harvest maximum amount of power due to ambient RF environment in which the FSS device is in. Pervasiveness of RF devices will allow eventual collection of power (switching does not need much power at all to do).
Sleep mode for Harvesting application, so that there is not a big current drain when not needed.
Automatic VSWR tuning or antenna matching, using FSS in cell phone -- create an impedance matching circuit in an IC with FSS.
Simple environment sense capability.
FSS in the device, say a phone, its sitting there, very cheap. When you put the cell phone down on the metal table, the FSS makes the table "disappear" by reflecting down. Try finite number of FSS settings to block out objects, heads, dielectric surfaces, metal surfaces. FSS built into the case of phone or laptop, with finite combinations of FSS settings for typical usage cases.
Demodulate with switching, in a low loss fashion. Make the FSS dark to move energy to a sideband. If multiple channels coming in on same carrier, FSS makes one visible, and let the interferencer be completely attenudate inband, using switch rate matched to modulation of the desired/undesired signals.
Generalize: Time Dependent, distributed FSS system. Low current switching no control. Binary changes of one or multiple switches.
Quanitzed fashion - capacitor banks switched in or out (low power!) If we make these in CMOS on chip, we can tune with capaticors, must need gate voltage, very low current MOS switch. Goes either into capacitor mode, or resistor in chip mode....Boundary condition of the antenna? Boundary of MOS? performance of MOS ? We have 2 states, what is the "condition" of the open and the short? May need to use 2 different banks of Capacitors, still virtually no current draw, but need clean open and clean short, or best we can get -- not likely to be clean at finer geometries. Finer geometries: Leakage is a problem. How to do? Loss of varactors at these frequencies? Need good Q, size of Gates matter.
Can use active amplifiers on each varactor to get Q multiplier and better Q. Prior art optics has FSS with only 3 cells per wavelength. This helps reduce to practice, may be more viable.
FSS on array can configure into end-fire antenna pattern, for use/applications in laptop or other dimension in form factor - can steer to edge. Possible use of FSS for MiMo and Beamsteering with end fire pattern.
FSS causes a time dependent spatial patter for array theory, practical gain in space, point beams to a particular place in 3D space, out away from antenna. You have power amp, and can do modulation on antenna. May be others doing this. Gabriel Rabiz (SD) David Rutledge (CalTech), Ramat Sami and Hajimiri (UCLA). Do space modulation, put info at a particular location. How can we transmit into a wireless channel, and make the channel crate both a xmtr and receiver? Holography? Headache is packaging dielectric lens which others are trying right now. Very low efficiency.
Low Profile transmission line antenna (like for 160m in 1985) - use the semiconductor or lossy conductor to serve as a "lossy ground' - this can allow us to do low profile antenna on chip.
For on chip antenna, Tune the loss in the ground or in the material between antenna and ground using FSS, and NOT the physical antenna elements (they stay etched as is). Punch holes in ground to get more loss, get sheet resistivity properly, can tune around the metal antenna element.
Use metal in process, hot making metal using wire bonds for circuits and antennas.