New Radiation Proof Transistor
Development of the New Type Radiation-Hardened Transistor for the Metal-Insulator-Semiconductor Integrated Circuits
Tech Area / Field
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
- PHY-SSP/Solid State Physics/Physics
3 Approved without Funding
Tbilisi State University, Georgia, Tbilisi
- Institute of Cybernetics, Georgia, Tbilisi
- Technical University of Valencia / Alcoy School of Engineering, Spain, Alcoy\nChristopher Newport University / Physics, USA, VA, Newport News
One of the main directions of modern microelectronics concentrates on developing high-reliability radiation-hardened integrated circuits (ICs) to be used in space, safety and control systems of nuclear power stations, medical instrumentation. The leading firms, which are defining the state-of-the-art in microelectronics, are developing new rad-hard products and converting their commercial-grade ICs into radiation-hardened versions to meet the needs of a fast approaching and growing market.
Metal-Insulator-Semiconductor (MIS) type field effect transistors are the most popular and most commonly used active components for the silicon ICs. The main advantages of MIS type transistors over other devices are: ultralow power consumption, design flexibility, ability to produce memory devices, small area, large signal swing, low cost and relative simplicity of the MIS technology. However their radiation-hardness is lower than that of bipolar transistors.
Ionising radiation primarily effects the gate-insulator of MOS devices. A part of the charge produced by radiation is trapped in the bulk of the dielectric and at its interface with Si causing long relaxation time instability and device performance degradation. While the mechanism of radiation failure of the traditionally used insulating films is reasonably well understood, a rational approach to producing radiation-hardened MIS devices has yet to emerge. The radiation hardness of current MIS ICs has been increased only up to 105 – 106 rad.
In 1997-1999 the ISTC Project #G-059 was carried out in our laboratory, which was aimed to develop the essentially new type insulating material for the radiation-hardened MIS ICs. Our new approach is based on the assumption that the stability of MIS structures will increase if an insulating film will be substituted by an amorphous, O and N doped Germanium film (GeOxNy film), with a wide energy gap and a high resistivity. In such material a certain amount of free carriers is existing and they have an anomalous low mobility. Movement of free carriers whose relaxation times are significantly shorter compensates the long relaxation time instability caused by the ionising irradiation.
The developed new type film forms a high quality interface with Si (Nss=2x1010 cm-2 eV-1) which is close to the best Si-SiO2 interface. The film is also characterised by a high value of dielectric constant (10) and a low density of bulk states (1016 cm-3).
No significant changes were observed after 108 rad -ray irradiation of Al/GeOxNy /Si MIS structures (Co60, D=5x105 rad/hour), and also after bias-aging (E= 4x105 V/cm) and bias-temperature stresses (300OC, 105V/cm, 20 min). The measured total dose immunity value for our MIS-structure exceeds that of the SiO2 based rad-hard MIS devices.
The purpose of this project is to manufacture the rad-hardened n- and p-channel MIS transistors and a simple rad-hardened IC –the CMIS inverter. The new type GeOxNy film will be used as the gate-insulator. These devices will be able to withstand 2-3 orders of magnitude higher total doses (107 – 108 rad(Si) when exposing to Co60 -ray) than modern rad-hardened MIS devices. The detailed technological chart will be developed for fabrication of radiation-hardened MIS transistors and CMIS inverters using GeOxNy films.
The project will be carried out in close collaboration with our foreign partners together with the Research and Production Association “MION” (Tbilisi, Georgia). Realization of the project objectives will allow us to fabricate unique, competitive and effective radiation-hardened MIS ICs on Si covering a wide range of civil products. All these will promote the integration of our scientists into the international scientific community and also help RPA “MION” in its future transition to a market-based economy. Most of the Project participants were actively involved in the development of the advanced microelectronic devices for the ballistic missiles and other delivery systems. Implementation of this Project will help to redirect their talents to peaceful activities.
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.