Investigation of Body-Tie Effects on Ion Beam Induced Charge Collection in Silicon-On- Insulator FETs using the Sandia Nuclear Microprobe

Silicon-on-insulator (S01) technology exhibits three main advantages over bulk silicon technology for use in radiation environments. (1) SOI devices are immune to Iatchup, (2)the volume of the sensitive region (body) and hence total charge collection per transient irradiation is much reduced in SOI devices and (3) the insulating layer blocks charge collection from the substrate (i.e., no fimneling effect). This effectively raises the single event upset threshold for the SOI device. However, despite their small active volume SOI devices are still vulnerable to single event effects (SEE). Inherent in the SOI transistor design is a parasitic npn bipolar junction transistor (BJT), where the source-body-drain acts as an emitter-base-collector BJT. An ion strike to a floating (not referenced to a specific potential) body can create a condition called snapback, where excess minority carriers in the drain-body junction forward bias the sourcebody junction, causing the parasitic BJT to turn on and inject current into the drain. Tying the body to the source limits the emitter-base current and reduces the sensitivity of the device to single ion strikes. Unfortunately, the body-tie loses effectiveness with distance due to resistivity, and in regions far enough from the tie the BJT is still in effect. Using the Sandia nuclear microprobe we have created charge collection maps of SOI FETs which have different body-tie designs. Comparisons of the experiment to DAVINCI simulations are also presented. Effects of body-ties and operating voltage on snap-back thresholds are also presented and predictions of performance in radiation environments made for the different designs.