Infoscience

Thesis

Compact modeling of high voltage MOSFETs

In the automotive industry, there is a strong trend that has increased the electronics in cars for various functions like fuel injection, electric control of doors and windows, electric chair adjustment, air conditioning etc. The 12V battery used in the present cars will not be sufficient for the increasing number of functions, as a consequence, a change towards 42V batteries will be necessary. For these automotive systems, so called smart power ICs must be used. These are the chips in which the power functionality e.g. control of motor is integrated with logic control. There is also a trend towards operation at high voltages and integrating more intelligence using a microcontroller's RAM/ROM memory and several other sensors and interfaces. The final goal is the integration of a complete system on a single chip, so called power system on chip (SoC). The interest in accurate modeling of high voltage transistors has increased in recent years due to the compatibility of these devices with standard CMOS technology. However, existing LDMOS models are not accurate enough for this task and SPICE models are specially weak for AC performance. The limitation of these models lies in their lack of capability to physically model some of the characteristic phenomena observed in high voltage devices. The increased difficulty is related to complex 2D effects specific to asymmetric high voltage device architectures. This thesis presents the compact modeling of high voltage devices. First, a highly scalable general high voltage MOSFET model, for the first time, is presented, which can be used for any high voltage MOSFET with extended drift region. This model includes physical effects like the quasi-saturation, impact-ionization and self-heating, and a new general model for drift resistance. The model is validated on the measured characteristics of two widely used high voltage devices in the industry i.e. LDMOS and VDMOS devices, and implemented in Verilog-A code and tested on commercial circuit simulators like SABER (Synopsys), ELDO (Mentor Graphics), Spectre (Cadence) and UltraSim (Cadence). The model exhibits excellent scalability with transistor width, drift length, number of fingers and temperature. Second, the compact modeling of lateral non-uniform doping is presented, which has great impact on the AC behavior. Third, the invalidity of Ward-Dutton charge partitioning scheme for lateral non-uniformly doped MOSFET is explained. A novel partitioning scheme is then developed and validated on the device simulation. For the first time, noise modeling of lateral non-uniformly doped MOSFET is carried out and validated on the device simulation.

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