TCAD Based SiGe HBT Advanced Architecture Exploration
Exploration d'architectures de transistors HBT SiGe à l'aide de l'outil TCAD
Résumé
The Impact of strain engineering technology applied on NPN-Si-BJT/NPN-SiGe-HBT devices on the electrical properties and frequency response has been investigated. Strain engineering technology can be used as an additional degree of freedom to enhance the carriers transport properties due to band structure changes and mobility enhancement. The mobility of charge carriers in bipolar devices can be enhanced by creating mechanical tensile strain in the direction of electrons flow to improve electron’s mobility, and by creating mechanical compressive strain in the direction of holes flow to improve hole’s mobility. Consequently, new devices concepts and novel device architectures that are based on strain engineering technology have been explored using TCAD modeling. The physical models and parameters used in TCAD simulations have been calibrated in collaboration with Bundeswehr University-Munich using Monte Carlo simulation. Specific models for SiGe bandgap, bandgap-narrowing, effective mass, energy relaxation, mobility for hydrodynamic and drift-diffusion simulations have been calculated and implemented in the house simulator using tabulated models compiled in C code. Two approaches have been used in this study to generate the proper mechanical strain inside the device. The first approach was through introducing strain engineering technology principle at the device’s base region using SiGe extrinsic stress layer. The second approach was through introducing strain engineering technology principle at the device’s collector region using strain layers. The study examined not only the transistor DC performance but also the RF performance through multiple optimizations for the explored vertical transistors. Simulation results showed that the strained silicon BJT/HBT devices exhibited better DC performance and high frequency characteristics in comparison with equivalent standard conventional BJT/HBT devices. An approximately 42% improvement in fT and 13% improvement in fMAX have been achieved for BJT device employing strain at the base region. As well, an enhancement of the collector current by nearly three times in strained silicon BJT device has been attained. The obtained results for applying the same technique on NPN-SiGe-HBT device have shown that applying strain on the base region of the HBT device is less efficient in comparison with the BJT device, as the SiGe base is already stressed due to the existence of Ge at the base. Moreover, utilizing a strain layer at the device’s collector region will result in an approximately 9%-14% improvement in fT and 7%-12% improvement in fMAX in comparison with an equivalent standard conventional NPN-SiGe-HBT device. Despite of the very small decrease in the breakdown voltage BV CE0 value (1% 4%), the fT×BVCE0 product enhancement is about 12% by means of strain engineering at the collector region.
The Impact of strain engineering technology applied on NPN-Si-BJT/NPN-SiGe-HBT devices on the electrical properties and frequency response has been investigated. Strain engineering technology can be used as an additional degree of freedom to enhance the carriers transport properties due to band structure changes and mobility enhancement. The mobility of charge carriers in bipolar devices can be enhanced by creating mechanical tensile strain in the direction of electrons flow to improve electron’s mobility, and by creating mechanical compressive strain in the direction of holes flow to improve hole’s mobility. Consequently, new devices concepts and novel device architectures that are based on strain engineering technology have been explored using TCAD modeling. The physical models and parameters used in TCAD simulations have been calibrated in collaboration with Bundeswehr University-Munich using Monte Carlo simulation. Specific models for SiGe bandgap, bandgap-narrowing, effective mass, energy relaxation, mobility for hydrodynamic and drift-diffusion simulations have been calculated and implemented in the house simulator using tabulated models compiled in C code. Two approaches have been used in this study to generate the proper mechanical strain inside the device. The first approach was through introducing strain engineering technology principle at the device’s base region using SiGe extrinsic stress layer. The second approach was through introducing strain engineering technology principle at the device’s collector region using strain layers. The study examined not only the transistor DC performance but also the RF performance through multiple optimizations for the explored vertical transistors. Simulation results showed that the strained silicon BJT/HBT devices exhibited better DC performance and high frequency characteristics in comparison with equivalent standard conventional BJT/HBT devices. An approximately 42% improvement in fT and 13% improvement in fMAX have been achieved for BJT device employing strain at the base region. As well, an enhancement of the collector current by nearly three times in strained silicon BJT device has been attained. The obtained results for applying the same technique on NPN-SiGe-HBT device have shown that applying strain on the base region of the HBT device is less efficient in comparison with the BJT device, as the SiGe base is already stressed due to the existence of Ge at the base. Moreover, utilizing a strain layer at the device’s collector region will result in an approximately 9%-14% improvement in fT and 7%-12% improvement in fMAX in comparison with an equivalent standard conventional NPN-SiGe-HBT device. Despite of the very small decrease in the breakdown voltage BV CE0 value (1% 4%), the fT×BVCE0 product enhancement is about 12% by means of strain engineering at the collector region.
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