Interface-trap Buildup Research Articles

Field dependence of interface-trap buildup in polysilicon and metal gate MOS devices

The electric field dependence of radiation-induced oxide- and interface-trap charge ( Delta V/sub ot/ and Delta V/sub it/) generation for polysilicon- and metal-gate MOS transistors is investigated at electric fields (E/sub ox/) from -4.2 MV/cm to +4.7 MV/cm. If electron-hole recombination effects are taken into account, the absolute value of Delta V/sub ot/ and the saturated value of Delta V/sub it/ for both polysilicon- and metal-gate transistors are shown to follow an approximate E/sup -1/2/ field dependence for E/sub ox/>or=0.4 MV/cm. An E/sup -1/2/ dependence for the saturated value of Delta V/sub it/ was also observed for negative-bias irradiation followed by a constant positive-bias anneal. The E/sup -1/2/ field dependence observed suggests that the total number of interface traps created in these devices may be determined by hole trapping near the Si/SiO/sub 2/ interface for positive-bias irradiation or near the gate/SiO/sub 2/ interface for negative bias irradiation, though H/sup +/ drift remains the likely rate-limiting step in the process. Based on these results, a hole-trapping/hydrogen transport model-involving hole trapping and subsequent near-interfacial H/sup +/ release, transport, and reaction at the interface-is proposed as a possible explanation of Delta V/sub it/ buildup in these polysilicon- and metal-gate transistors. >

Radiation-induced charge neutralization and interface-trap buildup in metal-oxide-semiconductor devices

Effects of switched bias on the radiation response of metal-oxide-semiconductor (MOS) devices have been investigated. Transistors with 50-nm gate oxides were irradiated at +10-V bias to create a large trapped-hole density in the oxide. Irradiation was continued under varying negative and positive biases. Very little radiation-induced charge neutralization is observed at biases <−10 V for these devices. However, significant trapped-hole neutralization is observed at biases from −10 to 0 V, with a broad maximum in neutralization rate from −6 to −1 V. The peak charge neutralization rate is approximately equal to the rate of trapped-hole buildup under positive bias. This establishes an upper bound on the rate of radiation-induced charge neutralization, and demonstrates that, under peak neutralization conditions, the effective cross section for the capture of radiation-induced electrons by a filled hole trap is similar to the effective cross section for capture of a hole by an empty trap. Interface traps are found to build up at approximately the same rate when the oxide electric field at the Si/SiO2 interface is positive, regardless of the field direction in the bulk of the oxide. This suggests that near-interfacial hydrogen may play a key role in interface-trap buildup in MOS devices.

Dose and energy dependence of interface trap formation in cobalt-60 and X-ray environments

The radiation-induced buildup of interface traps is examined on radiation-hardened 20-nm-gate-oxide n-channel transistors irradiated with /sup 60/Co and 10 keV X-rays. A variation in the fundamental dependence of interface-trap ( Delta D/sub it/) growth on dose from linear with dose to a square-root dependence was observed. The samples with the largest low-dose interface-trap buildup showed the slowest rate of growth (D/sup 1/2/), while the samples with the smallest low-dose Delta D/sub it/ showed the fastest buildup (linear with dose). A possible qualitative explanation of this behavior based on cluster centers is given. The interface-trap density growth was observed to tend toward saturation at doses above 3 Mrad (SiO/sub 2/). A photon energy dependence of D/sub it/ formation between /sup 60/Co and X-ray irradiation was not observed. >

Radiation-Induced Interface Traps in Power Mosfets

Methods for estimating radiation-induced interface trap density from the current-voltage (I-V) characteristics of MOSFETs are described and applied to commercially available power MOSFETs. The power MOSFETs show severe degradation on radiation exposure with the effects of positive oxide trapped charge dominating; however, interface trap buildup is significant. The results are compared to experimental measurements available on other technologies.