Lance Covert

RF Characteristics of Room-Temperature-Deposited, Small Gate Dimension Indium Zinc Oxide TFTs

Depletion-mode indium zinc oxide channel thin film transistors (TFTs) with gate dimension of 1 X 200 μm and drain-to-source distance of 2.5 μm were fabricated on glass substrates using radio frequency magnetron sputtering deposition at room temperature. Plasma-enhanced chemical vapor deposited SiN x was used as the gate insulator. The threshold voltage was around -2.5 V. Saturation current density at zero gate bias voltage was 2 mA/mm, and a maximum transconductance of 7.5 mS/mm was obtained at V ds = 3 V. The drain current on-to-off ratio was > 10 5 . The maximum field effect mobility measured in the saturation region was ∼ 14.5 cm 2 V -1 s -1 . A unity current gain cutoff frequency, f T , and maximum frequency of oscillation, f max of 180 and 155 MHz, respectively, were obtained. The equivalent device parameters were extracted by fitting the measured s parameters to obtain the intrinsic transconductance, drain resistance, drain-source resistance, transit time, and gate-drain and gate-source capacitance.

Simulation and measurement of a heatsink antenna: a dual-function structure

As the demand pushes for increasing chip densities, new mechanisms must be pursued in order to deal with problems such as heat dissipation. This is especially true for high-density three dimensional (3-D) packaging technology for RF devices. Though 3-D system-on-chip (SOC) technology shows promise for increasing chip densities, the heat generated by the RF transmitters power amplifier poses a threat to the devices. This paper proposes and evaluates a new type of antenna: a heatsink antenna, which simultaneously operates as a radiator of electromagnetic and thermal energy. A patch antenna was used in this study to evaluate the effect of a heatsink structure, though the actual dimensions and antenna/chip structure will depend on the particular system design. Measurements and simulation show that the heatsink lowers the resonant frequency of a patch antenna by 6.8% and 9.7%, respectively. In addition, simulations show that a poor radiation efficiency of the patch antenna fabricated on FR4 PCB can be improved significantly by a heatsink structure. For the antenna in this study, the heatsink improved the radiation efficiency from 33% to 62%.

Thermal simulations of three-dimensional integrated multichip module with GaN power amplifier and Si modulator

A finite-element simulation was used to quantitatively estimate the heat transfer in a three-dimensional multichip module (MCM) consisting of a GaN power amplifier with solder-bump-bonded Si modulator and integrated antenna on a high-resistivity SiC substrate under various conditions of power density and substrate and epi thicknesses via wire thickness and effective heat transfer coefficient. The maximum temperature in the integrated-antenna approach occurred in the center of the MCM. At a GaN power amplifier power level of 3W∕mm, a steady-state temperature of ∼125°C was reached in ∼20s. Bulk GaN substrates were also found to provide good thermal transfer characteristics, while sapphire produced an increase in temperature almost a factor of 3 higher than for SiC. At a power density of 10W∕mm, the steady-state operating temperature was ∼400°C even with SiC substrates.

AlGaN∕GaN high electron mobility transistors on Si∕SiO2/poly-SiC substrates

AlGaN∕GaN high electron mobility transistors were grown by molecular beam epitaxy on Si on poly-SiC substrates formed by the Smart Cut™ process. The Smart Cut™ approach is an alternative solution to provide both a high resistivity and an excellent thermal conductivity template needed for power applications. Although the structure has not been optimized, devices with 0.7μm gate length show breakdown voltage of >250V, fT of 18GHz, and fmax of 65GHz.

Thermal Considerations in Design of Vertically Integrated Si ∕ GaN ∕ SiC Multichip Modules

The thermal design of vertically integrated multichip modules (MCMs) based on GaN high electron mobility transistor (HEMT) power amplifiers (PAs) on SiC substrates with back-side heat-sink/antenna and Si modulators bonded to the common ground plane and PA chip using polydimethylsolixane (PDMS) is reported. The heat transfer in the integrated structure was estimated using finite element simulation for different PA power density, HEMT gate finger pitch, Si thickness, the presence or absence of the PDMS layer, and the thickness of dielectric isolation interlayers. The maximum temperature in the integrated antenna approach occurs near the gates of the HEMTs and hence the gate pitch has a strong effect on the temperature distribution. The presence of the PMDS has a major effect on the operating temperature of the PA and Si modulator, especially at high power densities, and also influences the temperature distribution within the MCM.

Dual-Function 3-D Heatsink Antenna for High-Density 3-D Integration

Radiation from heatsinks is typically undesirable and should be minimized to reduce electromagnetic interference (EMI). However, in certain applications such as high-power transmitters where both a heatsink and an antenna are required it can be advantageous to maximize the radiation from a heatsink by using the heatsink as the antenna. In this case, not only is the total component count in the transmitter reduced, but the heatsink can be beneficial to the antenna performance. A 2.4 GHz heatsink antenna based on a microstrip patch antenna design shows improved radiation efficiency and broader bandwidth. Also, the peak antenna gain is increased. This presentation reviews the idea of the heatsink antenna and how the heatsink can be exploited for improved antenna performance.