Peter Ledel Gammel

On-chip vacuum microtriode using carbon nanotube field emitters

We show a fully integrated, on-chip, vacuum microtriode fabricated via silicon micromachining processes using carbon nanotubes as field emitters. The triode is constructed laterally on a silicon surface using microelectromechanical systems (MEMS) design and fabrication principles. The technique incorporates high-performance nanomaterials in a MEMS design with mature solid-state fabrication technology to create miniaturized, on-chip power amplifying vacuum devices, which could have important and far-reaching scientific and technological implications.

A micromachined vacuum triode using a carbon nanotube cold cathode

A fully integrated on-chip vacuum microtriode using carbon nanotubes as field emitters was constructed laterally on a silicon surface using microelectromechanical systems (MEMS) design and fabrication principles. Each electrode in the triode was made of a hinged polycrystalline silicon panel that could be rotated and locked into an upright position. The device was operated at a current density as high as 16 A/cm/sup 2/. Although the transconductance was measured only at 1.3 /spl mu/S, the dc output power delivered at the anode was almost 40 /spl times/ more than the power lost at the grid electrode. The technique combines high-performance nano-materials with mature solid-state fabrication technology to produce miniaturized power-amplifying vacuum devices in an on-chip form, which could potentially offer a route of integrating vacuum and solid-state electronics and open up new applications for old-fashioned vacuum tubes.

Imaging of acoustic fields in bulk acoustic-wave thin-film resonators

By using an atomic-force-microscope-based technique, we image the vibration of high-frequency, bulk-mode, thin-film resonators. Our experimental technique is capable of monitoring the vibration of these devices over a broad frequency range, from 1 MHz to beyond 10 GHz, allowing us to obtain quantitative measurements of the piezoelectric properties of thin-film materials in that frequency range. This technique allows us to map the complex vibration modes of a new generation of high-frequency bulk piezoelectric resonators, revealing the presence of vibration patterns of very different characteristic lengths.

Condensed-matter physics. Why vortices matter.

In a magnetic field, a superconductor is threaded by swirling whirlpools of electric current. Understanding these magnetic vortices is important because they control the flow of current through the superconductor.

Method and apparatus for imaging acoustic fields in high-frequency acoustic resonators

This invention relates to a method and apparatus for imaging acoustic fields in high-frequency acoustic resonators. More particularly, the invention is directed to a scanning RF mode microscope system that detects and monitors vibration of high frequency resonators that vibrate in the frequency range of approximately 1 MHz to 20 GHz. The system then maps with sub-Angstrom resolution vibration modes of such devices and obtains quantitative measurements of the piezoelectric properties of the materials.

Improved electrical and thermal performance of ultra-thin RF LDMOS power transistors

We present the electrical and thermal performance of ultra-thin RF LDMOS devices. Following a proprietary process, we fabricated such devices with a thickness as reduced as 40/spl mu/m. This results in a reduction of the operating junction temperature, as demonstrated by infrared imaging experiments and three-dimensional finite-element-analysis simulations. As a result, the thermal resistance of our packaged devices reaches substantially lower values than industry standard. This allows for a higher power output and improved efficiency, as demonstrated by RF measurements.

Magnetostriction Of Charge Density Wave Superconductor

Single crystals of layered niobium diselenide (2H‐NbSe2) compound with hexagonally packed layers were studied in a range of temperature 1.5–300 K by measuring magnetostricrtion and magnetization in field up to 20 T. The data are compared with magnetic susceptibility measurements. Specific features of measured temperature and field dependences were observed near CDW transition temperature (32.5 K) and superconducting transition (7.2 K), sensitive to magnetic field direction and strength.

Ultra-thin RF LDMOS Power Transistors

We present the electrical and thermal performance of ultra-thin RF LDMOS devices. Following a proprietary process, we fabricated such devices with a thickness as reduced as 40¿m. This results in a reduction of the operating junction temperature, as demonstrated by infrared imaging experiments and three-dimensional finite-element-analysis simulations. As a result, the thermal resistance of our packaged devices reaches substantially lower values than industry standard. This allows for a higher power output and improved efficiency, as demonstrated by RF measurements.

Near-field microwave microscopy of thin film resonators

We present phase-sensitive, high spatial resolution, near-field microwave microscopy images of the rf fields radiated by piezoelectric resonators operating in the vicinity of 2 GHz. Near the resonance our data show a complex distribution of fields. We fit our data to the Butterworth/Van-Dyke model that describes the behavior of these devices, and find very good qualitative agreement. In general, we show the potential of this phase-sensitive near-field imaging technique to study the behavior of complex rf devices, with potential impact on the optimization of the devices design.