Uniform Thermal Distribution Research Articles

Thermally Stable Structure of InGaP/GaAs Hetero-junction Bipolar Transistor: Dual-Emitter Structure

We propose a new structure of InGaP/GaAs Hetero-junction Bipolar Transistor (HBT) with dual emitter fingers for power amplifier application, which is optimized for uniform thermal distribution within the device. The optimized thermal management of the proposed HBT relaxes the current decrease by a factor of 1.41 under active current bias, and prevents current gain collapse up to VCE of 8 V, while a conventional device shows a significant collapse at VCE=6.2 V.

Reliability and routability consideration for MCM placement

This paper presents a methodology based on the fuzzy logic approach for the placement of the power dissipating chips on the multichip module substrate. Our methodology considers both thermal distribution and routing length constraints during multichip module placement. In this paper, the main design issue is the coupled placement for reliability and routability. The objective of the coupled placement is to enhance the system performance and reliability by obtaining an optimal cost during multichip module placement. For reliability considerations, the design methodology is addressed on the placement of the power dissipating chips to achieve uniform thermal distribution. The thermal placement analysis is based on the modified fuzzy force-directed placement method. Placement for routability is based on minimizing the total wire length estimated by semi-perimeter method. The placement trade-off between routability and reliability is illustrated by varying a weighting factor. Case studies of the coupled placement are presented. In addition, the thermal distribution of the coupled placement results is simulated with the finite element method.

Recognition of volatile organic compounds using SnO 2 sensor array and pattern recognition analysis

A sensor array with 10 sensors integrated on a substrate was developed to recognize various kinds and quantities of volatile organic compounds (VOCs), such as benzene, toluene, ethyl alcohol, methyl alcohol, and acetone. The sensor array consists of gas-sensing materials using SnO 2 as the base material, plus a heating element based on a meandered platinum layer, all deposited on the substrate. The sensors on the sensor array are designed to produce a uniform thermal distribution and show a high and broad sensitivity and reproductivity to low concentrations through the usage of nano-sized sensing materials with high surface areas and different additives. By utilizing the sensing signals of the array with an artificial neural network, a recognition system can then be implemented for the classification and quantification of VOCs. The characteristics of the multi-dimensional sensor signals obtained from 10 sensors are analyzed using the principal component analysis (PCA) technique, and a gas pattern recognizer is implemented using a multi-layer neural network with an error-back-propagation learning algorithm. Simulation and experimental results demonstrated that the proposed gas recognition system is effective in identifying VOCs. For real-time processing, a DSP board can be used to implement the proposed VOC recognition system in conjunction with a neural network.

Explosive gas recognition system using thick film sensor array and neural network

A sensor array with nine discrete sensors integrated on a substrate was developed for recognizing the species and quantity of explosive gases such as methane, propane, and butane. The sensor array consisted of nine oxide semiconductor gas-sensing materials with SnO 2 as the base material plus a heating element based on a meandered platinum layer all deposited on the sensor. The sensors on the sensor array were designed to produce a uniform thermal distribution and show a high and broad sensitivity and reproductivity to low concentrations through the use of nano-sized sensing materials with high surface areas and different additives. Using the sensitivity signals of the array along with an artificial neural network, a gas recognition system was then implemented for the classification and identification of explosive gases. The characteristics of the multi-dimensional sensor signals obtained from the nine sensors were analyzed using the principal component analysis (PCA) technique, and a gas pattern recognizer was implemented using a multi-layer neural network with an error back propagation learning algorithm. The simulation and experimental results demonstrate that the proposed gas recognition system is effective in identifying explosive gases. For real time processing, a DSP board (TMS320C31) was then used to implement the proposed gas recognition system in conjunction with a neural network.

Thermal Placement Design for MCM Applications

This paper introduces an algorithm that focuses on the placement of the power dissipating chips for multichip module applications. The main design issue is addressed on the chip placement to achieve uniform thermal distribution. Our approach to the placement problem is based on the modified force-directed placement method. The proposed thermal force-directed placement method is to relate the force equations to the power dissipation values of the individual bare chip. Examples of multichip placement are presented. The finite element simulation results are also investigated and compared with quadrisection placement methods. [S1043-7398(00)01002-1]

Electrical and functional characterization of a novel self-biased linear silicon drift detector

We describe here a novel design of self-biased linear Silicon Drift Detector (SDD) which minimizes the dead area and ensures a uniform thermal distribution on the sensitive zone of the detector itself. The proper potential profile in the sensitive zone is established by the voltage drop along a single cathode which acts at the same time as a voltage divider and a field cathode. To verify the effectiveness of the novel working prinicple, a 2 × 3.4 cm 2 preliminary prototype has been manufactured by Canberra Semiconductor. The static and dynamic characteristics of the proposed device confirm that the spatial resolution (20 μm) is not affected by the convergence of the cathode-strips if the voltage drop along them is linear.

A novel cathode structure for a self-biased linear Silicon Drift Detector

A novel cathode structure for a self-biased linear Silicon Drift Detector (SDD) is presented. The proper potential profile inside the fully depleted substrate is established by the voltage drop along a single cathode implanted across each external surface and arranged as a zigzag. Compared to other self-biased linear SDDs, the proposed structure features a uniform thermal distribution and optimizes the sensitive area. The Poisson's equation together with the proper boundary conditions has been analytically solved in the 3D domain, and the solution has been validated by means of 3D simulation. A prototype based on this geometrical configuration has been manufactured at Canberra Semiconductor. The resistance spread of each portion which constitutes the implanted cathode has been measured and results within 2%.

Development of AC Calorimetric Method for Thermal Diffusivity Measurement V. Modulated Laser Beam Irradiation

In an ac light-irradiation method for measuring thermal diffusivity along the length of the rectangular thin film sample, we developed a method which uses a modulated laser beam. The laser beam was swept with a high frequency so as to cover the width of the sample. Such a procedure makes possible to obtain uniform ac thermal energy distribution in the direction perpendicular to the direction of ac temperature-wave propagation. Furthermore, it gives rise to a nonuniform ac thermal energy distribution in the direction along the direction of ac temperature-wave propagation. It is theoretically proven that the latter inhomogeneity does not affect the determination of thermal diffusivity. This fact is verified by experiment.

Computer-aided design and evaluation of novel catheters for conductive interstitial hyperthermia

Conductive interstitial heating is a modality in which heating elements are implanted directly into the treated tissue. One implementation of such therapy employs electrically heated catheters that are implanted in staggered, parallel rows. To explore strategies for maximising the uniformity of tissue temperature distributions achieved with heated catheters, a two-dimensional computer model with cylindrical co-ordinates was used to evaluate radially and longitudinally the temperature distributions produced by a typical interior catheter surrounded by other similar catheters. Insights from the computer model led to new designs for catheters containing multiple heating elements that produced more uniform thermal distributions, eliminating previous 'cold spots' within the treatment volume located near the ends of the catheter. The new catheter designs also include compartments for the optional placement of radioactive seeds for simultaneous thermoradiotherapy.

Correlation between fabrication processes and thermal distribution in medium power MESFETs

Correlation between fabrication process and thermal distribution was evaluated by means of high resolution IR thermography in two 0.5 W MESFET structures, having the same layout but differing in the presence of via hole connections. The via hole structure allows a great improvement in device thermal behaviour, with decrease in R tk and more uniform thermal distribution. The effect of process variations, such as gate misalignments, on temperature distribution within the device active area was also evaluated.