Capacitance-voltage characteristics of gamma irradiated Al2O3, HfO2, and SiO2 thin films grown by plasma-enhanced atomic layer deposition

Radiation-hardened electronics used in space, nuclear energy and radiation medicine applications require robust dielectric materials to be used as passivation layers and gate insulators. Thus, there is a need to understand the response of these materials under radiation exposure (e.g., gamma, neutron and proton) to develop radiation-tolerant and reliable electronic systems. In addition, as the size of transistors continues to scale down there is a need to have physically thicker dielectric layers with similar capacitance values to ultra-thin SiO₂. High permittivity (high-k) dielectrics lend themselves well to this task as they have capacitance values similar to ultra-thin SiO₂ while not facing issues of high leakage current and power dissipation as ultra-thin SiO₂. Atomic layer deposition (ALD) of thin films has gained interest in the development of radiation-hardened electronics as this process results in high quality (continuous and pinhole-free) and conformal gate dielectric thin films with precise thickness control to the angstrom level. Here, we examine the impact of gamma-irradiation on plasma-enhanced ALD dielectric layers using metal-oxide semiconductor (MOS) capacitors. In this work, three ALD gate dielectric films: Al₂O₃, HfO₂ and SiO₂ (between 22 and 24 nm thick) are utilized. The capacitance-voltage (C-V) response of plasma-enhanced ALD-based MOS capacitors upon gamma irradiation (Co-60) up to 533 krad without any shielding is observed. It is shown that ALD grown HfO₂ films are resistant to gamma irradiation based on the negligible shift in flat band voltage and hysteresis characteristics. Additionally, ALD grown Al₂O₃ films exhibited minimal generation of mobile traps but generation of trapped charges was observed. Furthermore, the flat band and hysteresis of ALD grown SiO₂ films showed development of both trapped and mobile charges which may suggest that this material lends itself to radiation dosimetry applications. These initial findings support the use of plasma-enhanced ALD grown films in the development of radiation-hardened electronics and sensors.