Modeling of reverse current effects in trench-based smart power technologies

Abstract

The increase in complexity in todays automotive products is driven by the trend to implement new features in the area of safety, comfort and entertainment. This significantly raises the safety requirements of new ICs and the identification of possible sources of failures gains in priority. One of these failure sources is the injection of parasitic currents into the common substrate of a chip. This does not only occur during exceptions in the operation of the IC but also affects applications which require switching of inductive loads. The difficulty to handle substrate current injection originates from its nonlocality as it potentially influences the entire IC.

In this thesis a point-to-point modeling scheme for Spice-based circuit simulation is proposed. It addresses parasitic coupling effects caused by minority carrier injection into the substrate of a deep-trench based BCD technology. Since minority carriers can diffuse over large distances in the common substrate and disturb circuits in their normal operation, a quantitative approach is necessary to address this parasitic effect early during design. An equivalent circuit based on the chip's design is extracted and the coupling effect between the perturbing devices and the susceptible nodes is represented by Verilog-AMS models. These models represent the three main components in the coupling path which are the forward biased diode at the perturbing device, the reverse biased diode at the susceptible node, and the intermediary common substrate of the chip. An automated layout extraction framework identifies the injectors of the minority carriers and the sensitive devices. Additionally, it determines the relevant parameters for the models. The curve fitting functions of the models are derived from calibrated TCAD simulations which are based on the measurement results of two dedicated test chips.

The test chips were specifically designed to provide detailed analysis capabilities of this parasitic coupling effect. This led to a design which contains several different injector nodes and a large number of susceptible nodes spread over the entire area of the chip. Additionally, the chip incorporates the most commonly used layout-based guard structures to obtain an in-depth insight on their efficiency in recent BCD technologies.

Based on the results obtained by measurements of the test chips the underlying physics of the coupling effect are discussed in detail. Minority carrier injection in the substrate is not much different to the operating principle of a bipolar transistor and the differences and similarities between them are presented. This forms the basis of the model development and explains how the equations of the Verilog-AMS models were derived. Finally, the entire simulation flow is evaluated and the simulation results are compared to measurements of the chip.