CHARGE COLLECTION AND SEU MECHANISMS

In the interaction of cosmic ions with microelectronic devices a dense electron hole plasma is created along the ion track. Carriers are sep arated and transported by the electric field and under the action of t he concentration gradient. The subsequent collection of these carriers induces a transient current at some electrical node of the device. Th is ''ionocurrent'' (single ion induced current) acts as any electrical perturbation in the device, propagating in the circuit and inducing f ailures. In bistable systems (registers, memories) the stored data can be upset. In clocked devices (microprocessors) the parasitic perturba tion may propagate through the device to the outputs. This type of fai lure only affects the information, and do not degrade the functionnali ty of the device. The purpose of this paper is to review the mechanism s of single event upset in microelectronic devices. Experimental and t heoretical results are presented, and actual questions and problems ar e discussed. A brief introduction recalls the creation of the dense pl asma of electron hole pairs. The basic processes for charge collection in a simple np junction (drift and diffusion) are presented. The funn eling-field effect is discussed and experimental results are compared to numerical simulations and semi-empirical models. Charge collection in actual microelectronic structures is then presented. Due to the par asitic elements, coupling effects are observed. Geometrical effects, i n densely packed structures, results in multiple errors. Electronic co uplings are due to the carriers in excess, acting as minority carriers , that trigger parasitic bipolar transistors. Single event upset of me mory cells is discussed, based on numerical and experimental data. The main parameters for device characterization are presented. From the p hysical interpretation of charge collection mechanisms, the intrinsic sensitivity of various microelectronic technologies is determined and compared to experimental data. Scaling laws and future trends are fina lly discussed.