Effects of pre-irradiated thermal treatment on ideal factor of excess base current in bipolar transistors

Abstract

<sec>During the service of the spacecraft, it will be disturbed by the energetic particles and rays, and thus induce total ionizing dose (TID), displacement damage (DD) or single event effect (SEE) to generate inside the electronic system, which can seriously affect the service lifetime of the electronic components. The difference in structure and types of electronic components are less sensitive to the radiation effects, but bipolar transistor is strongly sensitive to ionizing radiation effect. As a basic component of bipolar circuits, the in-depth study of bipolar transistor ionization radiation effect is of significance for engineering.</sec><sec>It has been shown that the an amount of hydrogen can inevitably introduced from an external source during the sealing process of the devices. The KOVAR alloy is widely used as a metal cap material of bipolar transistor in the process of encapsulation. The residual gas analysis (RGA) for sealed Kovar lid packages is shown to have 1%–2% of the hydrogen in the cavity. The source of the hydrogen is generally considered to be out-gassing from the gold plating on the KOVAR. So far, the researches have focused on the study of the ionization damage effect of bipolar transistors with different structures under ⁶⁰Co gamma ray irradiation. There is lack of systemic study on the comparison of transistors packaged with and without cap.In this paper, we study the influence of sealed KOVAR lid packaged on ionizing radiation damage of lateral PNP bipolar transistor (LPNP) by using ⁶⁰Co gamma ray as an irradiation source. The semiconductor parameter analyzer is used to measure the electrical parameters of LPNP transistor during irradiation. The irradiation defects in LPNP transistors packaged with and without cap are characterized by deep level transient spectroscopy (DLTS). Experimental results show that the LPNP transistors packaged with and without cap have similar electrical characteristics. The base current increases with the total dose increasing, while the collector current remains almost constant. The degradation of LPNP transistor packaged with cap is more serious.</sec><sec>According to the excess base current varying with base-emitter voltage for the LPNP transistors packaged with and without cap, the degradation of bipolar transistor packaged with cap is more serious under the same irradiation conditions. According to the analysis of DLTS, comparing with bipolar transistor packaged without cap, the signal peak at about 300 K is shifted to the left for the bipolar transistor packaged with cap. These results indicate that the LPNP transistors packaged with cap can generate more interface states during irradiation, which is attributed to a large amount of hydrogen and water vapor out-gassing from the gold plating on the KOVAR, which is released under the thermal stress. In the sealed environment, hydrogen can only diffuse into the device cavity, and is combined with the metal material in the transistor to form metal hydride. Therefore the degradation of transistor is severe under the same irradiation condition.</sec>