Amit Kumar Sahoo

A Scalable Electrothermal Model for Transient Self-Heating Effects in Trench-Isolated SiGe HBTs

This paper demonstrates a scalable electrothermal model for transient self-heating effects in trench-isolated SiGe heterojunction bipolar transistors (HBTs). The scalability of the thermal model has been investigated by considering pyramidal heat diffusion approximation between the heat source and the thermal ground. Three-dimensional thermal TCAD simulations have been carried out to obtain transient variations of the junction temperature and to extract the thermal impedance in the frequency domain. A recursive thermal network with scalable model parameters has been developed and added at the temperature node of the HBT compact model HiCuM. This network has been verified through numerical simulations and by low-frequency s-parameter measurements and found to be in excellent agreement for various device geometries.

Thermal Impedance Modeling of Si–Ge HBTs From Low-Frequency Small-Signal Measurements

In this letter, the thermal impedance of SiGe heterojunction bipolar transistors has been characterized using low-frequency small-signal measurements. Theoretical works for thermal impedance modeling using different electrothermal networks, developed until date, have been verified with our experimental results. We report for the first time the experimental verification of the electrothermal model for thermal impedance developed by Mnif using a nodal and recursive network. A generalized expression of the frequency-domain thermal impedance has been selected for electrical compact transistor model (HiCuM) improvement, parameter extraction, and electrothermal network verification.

A Geometry Scalable Model for Nonlinear Thermal Impedance of Trench Isolated HBTs

This letter presents a geometry scalable approach for the calculation of temperature dependent thermal impedance (ZTH) in trench-isolated heterojunction bipolar transistors. The model is capable of predicting the ZTH at any desired temperature and bias points. The temperature dependency is derived by discretizing the heat flow region into n number of elementary slices depending on the thermal gradient. Temperature dependent thermal resistances Rths and capacitances Cths for each of the slices are calculated in a self-consistent manner. Finally, the proposed model is validated with low-frequency measurements at different ambient temperatures (Tamb) for different transistor geometries and found to be in good agreement.

A scalable model for temperature dependent thermal resistance of SiGe HBTs

This paper presents a geometry scalable approach for temperature dependent thermal resistance (RTH) calculations in trench-isolated SiGe heterojunction bipolar transistors (HBTs). The model is able to predict the RTH at any temperature and power dissipation (Pdiss). The temperature dependency is obtained by discretizing the heat flow region into n-number of elementary slices depending on the temperature gradient. RTHs of each slice are calculated using temperature dependent thermal conductivity. The results are compared to 3D thermal TCAD simulations for a wide range of ambient temperature (Tamb), Pdiss and device dimensions. Finally, the scalability is validated through measurements of several transistor geometries as well as two different technologies and found to be in good agreement.

A study on transient intra-device thermal coupling in multifinger SiGe HBTs

This paper presents a study of transient mutual thermal coupling occurring between the fingers of trench isolated SiGe HBTs. Three-dimensional thermal TCAD simulations have been carried out to obtain the temperature evolution in transient operation in a multifinger HBT structure. The same behavior has been simulated using a netlist-based model, which provides an accurate representation of the substrate thermal coupling between active device areas. On-wafer measurements in pulsed conditions have been conducted on specially designed test structures that permit to determine the thermal coupling between the different fingers of a 5x(CBEBC) SiGe HBT; the results from the measurements are found to be in good agreement with a simulation in which the thermal coupling network has been added to the thermal nodes of five HiCuM transistor models.

Electro-thermal characterization of Si-Ge HBTs with pulse measurement and transient simulation

This paper describes a new and simple approach to accurately characterize the transient self-heating effect in Si-Ge Heterojunction Bipolar Transistors (HBTs), based on pulse measurements and verified through transient electro-thermal simulations. The measurements have been carried out over pulses applied at Base and Collector terminals simultaneously and the time response of Collector current increase due to self-heating effect are obtained. Compared to previous approach, a complete calibration has been performed including all the passive elements such as coaxial cables, connectors and bias network. Furthermore, time domain junction temperature variations, current of heat flux and lattice temperature distribution have been obtained numerically by means of 3D electro-thermal device simulations. The thermal parameters extracted from measurements using HiCuM HBT compact model have been verified with the parameters extracted from electro-thermal transient simulation. It has been shown that, the standard R-C thermal network is not sufficient to accurately model the thermal spreading behavior and therefore a recursive network has been employed which is more physical and suitable for transient electro-thermal modeling.

Optimized Ring Oscillator With 1.65-ps Gate Delay in a SiGe:C HBT Technology

In this letter, we report a record gate delay of 1.65 ps of a current-mode logic ring oscillator (RO) fabricated with an advanced SiGe:C heterojunction bipolar transistor technology. Outstanding performance has been achieved through process and layout optimization and inductive peaking in series with the load resistor. The RO operates at a single-ended voltage swing of 200 mV. The transistors used in the RO exhibit a peak transit frequency fT of 310 GHz and a peak maximum oscillation frequency fmax of 400 GHz. To the best of our knowledge, a gate delay of 1.65 ps is the fastest result for a bipolar transistor-based technology.

Characterization of intra device mutual thermal coupling in multi finger SiGe:C HBTs

This paper studies the mutual coupling in trench isolated multi-emitter bipolar transistors fabricated in a Si/SiGe:C HBT technology STMicroelectronics featuring fT and fmax of ~300GHz and ~400GHz, respectively. Thermal coupling parameters are extracted using three-dimensional (3D) thermal TCAD simulations. The obtained parameters are implemented in a distributed transistor model that considers self-heating as well as thermal coupling between emitter fingers. Very good agreement is achieved between circuit simulations and DC measurements carried out on an in-house designed test structure.

Electro-thermal dynamic simulation and thermal spreading impedance modeling of Si-Ge HBTs

In this paper, a new and simple approach simulating electro-thermal dynamic behaviour of Heterojunction Bipolar Transistors (HBTs) has been demonstrated. Time domain junction temperature variations at different frequency and, therefore, thermal spreading impedance have been obtained numerically by means of 3D device simulations and which has been verified through low frequency scattering parameter measurements for different geometry of transistors. A physical electro-thermal recursive network has been employed for HiCuM compact model simulation and thermal parameters extraction.

Characterization of mutual heating inside a SiGe ring oscillator

This paper reports on the electrical and thermal characterization of a state of the art SiGe ring oscillator (RO) with 2.2 ps gate delay fabricated in a Si/SiGe:C technology featuring fT and fmax of ~300 GHz and ~400 GHz, respectively. The transistor model is verified through DC and RF characteristics taken from the same die as the circuit measurements. Excellent agreement between measurements and compact model simulation is shown. A simple method is presented that calculates the nonlinear circuit temperature rise in the local circuit area resulting from mutual heating of all active and passive components. Once taken into account the circuit temperature, the accuracy of circuit simulation is significantly improved.