H. Safar

Distributed effects in high power RF LDMOS transistors

This paper focuses on the effects of distributed RF transmission lines on performance aspects, such as, gain, output power, efficiency etc. in high power RF LDMOS amplifiers. The methodology to model and capture the distributed effects is discussed. Suitable alternatives to mitigate power loss due to distributive effects in large transistors are presented. Also, the contributions of the package to the overall device performance are addressed.

Power transistors fabricated using isotopically purified silicon (/sup 28/Si)

It is well known that isotopic purification of group IV elements can lead to substantial increases in thermal conductivity due to reduced scattering of the phonons. The magnitude of the increase in thermal conductivity depends on the level of isotopic purification, the chemical purity, as well as the test temperature. For isotopically pure silicon (/sup 28/Si) thermal conductivity improvements as high as sixfold at 20 K and 10%-60% at room temperature have been reported. Device heating during operation results in degradation of performance and reliability (electromigration, gate oxide wearout, thermal runaway). In this letter, we discuss the thermal performance of packaged RF LDMOS power transistors fabricated using /sup 28/Si. A novel technique allows the cost effective deployment of this material in integrated circuit manufacturing. A clear reduction of about 5/spl deg/C-7/spl deg/C in transistor average temperature and a corresponding 5%-10% decrease in overall packaged device thermal resistance is consistently measured by infrared microscopy in devices fabricated using /sup 28/Si over natural silicon.

The nature of the magnetic flux behavior of the superconductor LaSrcuO

Abstract Precise magnetization measurements in La1.85Sr.15CuO4 from 1.5K to 40K and from 1 mOe to 300 Oe show that the magnetic flux penetration can be understood in terms of a simple critical state model, applied to a multiple connected non homogeneous superconductor. The magnetization data together with the results from vibrating reed experiments show that the magnetic flux penetration at the lowest fields is not associated with superconducting vortices. The vortices penetrate at a field Hcl characteristic of the regions where the order parameter has its maximum value.

High performance RF power LDMOSFET technology for 2.1GHz power amplifier applications

Silicon RF LDMOSFET technology is demonstrated with excellent RF performance. It achieves high power gain of 14.5dB with a high power of 130W at 2.1GHz. Its high efficiency and high linearity makes it highly desired for base station applications. 2mil substrate enables the best-in-class of thermal stability. Low HCI effect, integrated ESD and gold metal ensure high long-term reliability.

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.

Logarithmic to nonlogarithmic flux creep transition and magnetic flux hardening in BiSrCaCuO superconducting ceramics

Abstract A sharp temperature and field dependent transition from a logarithmic to a non-logarithmic flux creep behavior has been found in BiSrCaCuO superconductors. The transition is not followed by any noticeable change in the magnetization. However, vibrating reed measurements show that it coincides with a strong hardening of the magnetic structure. The transition occurs at fields and temperatures well below the reversibility line. The possible relation to the recently proposed flux lattice melting is discussed.

PERCOLATION AND GLASS BEHAVIOR IN CERAMIC SUPERCONDUCTORS: OXYGEN EFFECTS

It is shown that small variations of oxygen content in La1.8Sr0.2CuO4−δ can be used to control the reversible and irreversible magnetization temperature dependence of the superconducting state. A grain bond model is appropriate to describe the superconducting response of the ceramics. The study of the temperature dependence of the magnetization and the resistive transition temperature, in a slightly deoxygenated sample, show that the reversible superconducting state is strongly correlated to superconducting percolation. Deoxygenation has been shown to be an excellent technique to study the time evolution of metastable states induced by currents in the bonds and or in the grains. It is shown that superconducting grains are not correlated to ceramic grains.

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.