Radiation Tolerant Devices Research Articles

Proton radiation effects on electronic defect states in MOCVD-grown (010) β-Ga2O3

The impact of 1.8 MeV proton irradiation on metalorganic chemical vapor deposition grown (010) β-Ga2O3 Schottky diodes is presented. It is found that after a 10.8×1013cm−2 proton fluence the Schottky barrier height of (1.40±0.05 eV) and the ideality factor of (1.05±0.05) are unaffected. Capacitance–voltage extracted net ionized doping curves indicate a carrier removal rate of 268±10cm−1. The defect states responsible for the observed carrier removal are studied through a combination of deep level transient and optical spectroscopies (DLTS/DLOS) as well as lighted capacitance–voltage (LCV) measurements. The dominating effect on the defect spectrum is due to the EC-2.0 eV defect state observed in DLOS and LCV. This state accounts for ∼75% of the total trap introduction rate and is the primary source of carrier removal from proton irradiation. Of the DLTS detected states, the EC-0.72 eV state dominated but had a comparably smaller contribution to the trap introduction. These two traps have previously been correlated with acceptor-like gallium vacancy-related defects. Several other trap states at EC-0.36, EC-0.63, and EC-1.09 eV were newly detected after proton irradiation, and two pre-existing states at EC-1.2 and EC-4.4 eV showed a slight increase in concentration after irradiation, together accounting for the remainder of trap introduction. However, a pre-existing trap at EC-0.40 eV was found to be insensitive to proton irradiation and, therefore, is likely of extrinsic origin. The comprehensive defect characterization of 1.8 MeV proton irradiation damage can aid the modeling and design for a range of radiation tolerant devices.

Highly radiation-tolerant polymer field-effect transistors with polystyrene dielectric layer

There is high demand for radiation-tolerant devices for use in electronic applications in extreme irradiation environments, but conventional silicon transistors cannot satisfy the device requirements. In this work, we systematically investigated the total ionizing dose (TID) responses of polymer field-effect transistors (PFETs). By selecting suitable polymer gate dielectric materials (especially PS), it is found that these PFETs show significantly improved tolerances to the TID. Specifically, a PFET fabricated using polystyrene as its gate dielectric layer can maintain more than 95% of its electrical performance even after exposure to a TID of 7.5 Mrad (SiO2). The irradiated device has a long shelf lifetime that exceeds 1000 days. Simple inverter circuits were also fabricated and also demonstrated tolerance to a high TID of 7.5 Mrad. This work provides a possible solution for the development of PFETs for applications in extreme irradiation environments.

Tin diffusion in germanium: a thermodynamic approach

Point defect properties including diffusion properties are technologically important in semiconductor materials particularly as the characteristic dimension of devices are a few nanometers. Tin is an isovalent dopant in germanium that is presently considered to form radiation tolerant devices and in defect engineering strategies aiming to contain the high n-type dopant diffusion. In the present investigation we show that the cBΩ thermodynamic model linking the defect Gibbs energy to the isothermal bulk modulus and the mean volume per atom, can describe tin diffusion in germanium. The model is used to calculate point defect thermodynamic parameters such as the activation entropy, activation enthalpy and activation volume of tin diffusion in germanium as a function of temperature.

LED Technologies for Optocouplers: Fundamental Issues and Hardness Assurance

Radiation damage is examined for several different LED technologies used in optocouplers, including those with wavelengths near 700 nm that are used in radiation-tolerant devices, and have not been widely studied. Forward diode characteristics and reverse recovery time measurements are examined as potential parameters for hardness assurance.

Accurate numerical models for simulation of radiation events in nano-scale semiconductor devices

Space and ground-level electronic equipment with devices of nanometer scale and extremely high densities may be strongly affected by ionizing radiation. Accurate numerical models are necessary for better analysis of radiation effects and design of radiation tolerant devices. Numerical models and adaptive dynamic 3D mesh generation presented in this paper enable efficient simulations of transient semiconductor device response to realistic multi-branched track, produced by ionizing particle and nuclear reactions. A description of the numerical models, adaptive 3D meshing approach, and efficient solution method for large 3D problems using unstructured meshes is provided. The developed approach efficiently uses computer resources, which makes possible solution of transient 3D multi-branched ion strike problems with 100,000 mesh nodes within 512MB computer memory.

Proton Radiation Effects on Nanocrystal Non-Volatile Memories

We report on proton radiation effects on Si-nanocrystal (Si-NCs) MOS capacitors and nMOS transistors aiming at non-volatile memory applications. Irradiation experiments were conducted on NC MOS capacitors using protons of 1.5 MeV and 6.5 MeV and on NC nMOS transistors using protons of 1.5 MeV. The range of doses investigated was ~ 1 to ~ 100 Mrad (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). A 2-D layer of Si NCs with ~ 3 nm mean diameter and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> surface density was successfully achieved by low-energy (1 keV) ion-beam-synthesis in thin SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers. After irradiation, programmed capacitors are found to undergo bit flip while programmed transistors are not. Charge retention measurements at room temperature for the write and erase states of irradiated and non-irradiated samples reveal that a significant memory window exists at an extrapolated time of ten years even after an irradiation dose as high as 120 Mrad (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The flat-band decay rate of the erase state in NC MOS capacitors does not depend on the irradiation-dose while the opposite occurs for the write state which is found to be directly dependent on D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> values after irradiation. These results clearly indicate that NC non-volatile memories (NVM) are promising radiation tolerant devices.

Irradiation Effects in Space Solar Cells Made of Multiple Absorbers

AbstractSolar cells made of multiple absorbers are a commonly used approach for improving efficiency due to their extended range of spectral sensitivity. Indeed, efficiencies nearing the theoretical maximum have been achieved with a triple-junction device made of In0.51Ga0.49P (InGaP2), GaAs, and Ge solar cells connected in series. For extraterrestrial applications, there is the added requirement of radiation tolerance. The main challenge for space power-generation is therefore the development of highly efficient and radiation-tolerant devices. We have investigated several aspects of the radiation response of solar cells made of multiple absorbers, such as multijunction devices and quantum-well solar cells. Novel possibilities such as quantumdot solar cells and ordered-disordered heterostructures are proposed.

Materials study of silicon-on-lnsulator material by TEM

Silicon-on-insulator (SOI) technology addresses the need for many different device applications, such as radiation tolerant devices, high voltage, and three-dimensional circuitry applications. Isolated silicon epitaxy (ISE) is a commercialised process which results in excellent SOI material quality with proven results, having overcome most of the obstacles of other processes, although only having reduced, not eliminated, threading dislocations. The remaining isolated dislocations have been examined in detail by transmission electron microscopy (TEM). These have been diagnosed as normal lattice dislocations, with no faults or twins in the material. The nature, source, and behavior of the remaining dislocations is discussed.

Overview

Background Silicon-on-insulator (SOI) materials provide an emerging technology for high-density, high-performance, special-purpose integrated circuits (ICs). These useful SOI properties are fundamentally derived from the capability of total electrical isolation of silicon areas and from the qualitative reduction of junction areas. We illustrate this in Fig. 1, where a bulk complementary MOS cross section is compared to an equivalent SOI structure. Bulk CMOS is used for comparison since the most likely initial impact of SOI is special-purpose integrated circuits, such as three-dimensional circuits, high-voltage transistors, or radiation-tolerant devices. The extraordinary success for dynamic RAM technology presents a formidable barrier for any new competitor in packing density, whereas, in other areas, SOI has special characteristics that will provide it with some advantage.