Novel Diffusion-Drift Model for Evaluating Impact of Ionizing Radiation on Microelectronic Devices

Achieving a reduction of the size of the active regions of diode and transistor structures is the main trend in the development of hardware components for digital and analog electronic equipment.

This can be accomplished by enhancing the performance characteristics of micro- and nanoelectronics devices (increasing power and operating frequencies, increasing their memory and speed, noise reduction, and also) while maintaining production costs at the same level or even reducing them. Analogous processes (with a specific time lag) also occur during the development of exclusive hardware elements designed for application in space systems.

Electronic devices are adversely affected by the ionizing radiation in outer space, leading to a reduction in service life and unexpected malfunctions or failures. The amount of testing can be reduced through mathematical modeling of the response of such elements to the impacts of ionizing radiation from outer space, ultimately reducing the overall cost as well as the time needed to develop micro- and nanoelectronics devices.

However, when it comes to modern microwave semiconductor devices including submicron active regions, simple and analytical numerical models based on the linear superposition of radiation effects usually fail since the dynamics of physical processes in such devices is non-linear and complex.

The movement of charge carriers—holes and electrons—inside semiconductor devices developed based on outdated topological standards with specifications for hundreds of nanometers (for comparison, the topological standards of modern processors are 10 nm) is a diffusion-drift process—a slow displacement under the impact of an electric field against chaotic scattering on different inhomogeneities. In such a case, the system exists in a locally equilibrium state, and can be described from the point of view of classical statistical physics and thermodynamics.

By contrast, transport of particles in submicron semiconductor devices is quasiballistic, that is, their motion is largely directional, sparse scattering disrupts the gain in the velocity of particles in the electric field. In such a case, the system is in a deep nonequilibrium state and its thermodynamic parameters (for example, the temperature of the electron-hole plasma) stay, to be precise, undetermined.

Conventional charge carrier transport models are based on local-equilibrium diffusion drift or quasi-hydrodynamic approximations developed over 50 years ago. Yet, the reduction in size of the active region of modern semiconductor structures to the energy and momentum relaxation length of the electron-hole plasma (20–50 nm for Si and GaAs under normal conditions) and the reduction in flight time through the active region to a duration of the order of the energy and momentum relaxation time of electron-hole plasma (0.1–0.2 ps for Si and GaAs under normal conditions) lead to violation of the condition of locality, which results in an increase in the error while calculating the characteristics of the elements.

Investigation of the response of the submicron structures to the impacts of ionizing radiation from outer space additionally mandates considering the heterogeneity of ionization and defect formation, and also the stochastic nature of the interaction of radiation and particles with matter. Consequently, the model of gradual degradation of the macroscopic properties of a semiconductor turns irrelevant. Hence, in the case of submicron structures, the probabilistic model of unexpected radiation failures becomes desirable.

Alexander Puzanov, Associate Professor at the UNN Department of Quantum Radiophysics and Electronics, stated that scientists from Lobachevsky University collaborated with their colleagues from the Institute of Physics of Microstructures of the Russian Academy of Sciences to propose a diffusion-drift model in a locally non-equilibrium approximation for investigating the excitation relaxation in an electron-hole plasma under the impact of heavy charged particles from outer space or of laser radiation that mimic them.

It was shown that the locally nonequilibrium model has a wider application range for describing fast relaxation processes, in particular, it accurately takes into account the ballistic velocity of charge carriers, which is necessary to calculate the current flowing in semiconductor structures when they are exposed to heavy charged particles from outer space. It can also be used to determine the probability of failure and malfunction of micro- and nanoelectronics devices.

Alexander Puzanov, Associate Professor, UNN Department of Quantum Radiophysics and Electronics

At present, efforts are ongoing to develop the locally nonequilibrium model of charge carrier transport in the areas mentioned below:

  • Formulation of a locally nonequilibrium quasi-hydrodynamic model
  • Calculation of the properties of submillimeter-frequency multipliers based on Schottky diodes
  • Substantiation of the model through the comparison of simulation results with experimental data

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