Radiation Induced Charge Neutralization Research Articles

Numerical modeling of radiation-induced charge neutralization in MOS devices

Radiation-induced charge neutralization at different bias is studied for 230 nm p-channel MOS dosimeters under γ-radiation. A physics-based numerical model is employed to reproduce the experimental results. Good agreement is obtained between measurements and simulations considering capture and neutralization rates independent of electric field during neutralization stages. Sensitivity curves during neutralization stages show a two part process consisting of a slow decrease for short times followed by a rapid fall. Remarkably, the model predicts this behavior and allows to understand that in terms of the potential well generated due to trapped holes within the oxide.

Long Term Effects of Charge Redistribution in Cycled Bias Operating MOS Dosimeter

Techniques based on bias switching during the irradiation allow to extend the measurement range of MOS dosimeters. The response of the REM RFT300 RADFET dosimeter during bias cycled measurements shows a slow shift of the quasi-steady state threshold voltage value during radiation-induced charge neutralization. This phenomenon was previously explained as due to the presence of border traps. In this work, a recently developed numerical model which included the main physical processes leading to hole trapping and neutralization in MOS oxides was used to reproduce this experiment. The application of the model shows that the slow shift of the quasi-steady state threshold voltage during neutralization stages is a consequence of the spatial redistribution of trapped charge within the oxide. The effect this phenomenon has on MOS dosimetry is analyzed.

Influence of Alternate Biasing on TID Effects of Irradiated Mixed-Signal Programmable Arrays

This work investigates the influence of alternate biasing on TID effects in mixed-signal programmable devices. By reducing the time the device is biased when exposed to ionizing radiation, the severity of TID effects is also reduced, due to the increasing in the initial recombination of electron-hole pairs and the radiation induced charge neutralization effect. These effects are investigated considering a switched capacitor filter prototyped in a Field Programmable Analog Array. Eight samples of such device were exposed to gamma radiation while the devices were alternately biased, by repeatedly turning the power on and off, corresponding to different equivalent total biasing times and duty-cycles. Results show increase in radiation tolerance to the alternate biased devices, which is dependent also on the biasing duty-cycle. Considering this behavior, a novel system level radiation hardening technique, based on modular redundancy, associated to an alternate biasing scheme, is also proposed in this paper.

Conversion model of the radiation-induced interface-trap buildup and its hardness assurance application

The model, which confirms that the interaction of trapped positive charges (hydrogenous species) in the oxide and electrons from the substrate is an important component of radiation-induced interface-trap buildup, is presented. The “one-to-Koi” relationship between the number of trapped holes annealed and number of interface-trap generated is used for prediction of MOS device response in space environment. The model of enhanced low dose rate effect (ELDRS) is proposed. ELDRS conversion model is based on the assumption that there are two types of traps: shallow and deep. The time constants of these traps are different and correspond to interface-trap buildup at high dose rates for shallow traps and at low dose rates for deep traps. The possible physical mechanism of ELDRS effect elimination in the silicon-germanium (SiGe) bipolar transistors is described. The original mechanism of interface-trap buildup saturation based on radiation-induced charge neutralization (RICN) effect is presented.

Effect of Radiation Induced Charge Neutralization on ELDRS

The physical model, procedure of fitting parameter extraction and experimental study of the contribution of radiation induced charge neutralization (RICN) effect on enhanced low dose rate sensitivity (ELDRS) of bipolar devices are presented.

Mechanism of the Saturation of the Radiation Induced Interface Trap Buildup

Ionizing radiation impact leads to degradation of electrical parameters of microelectronic devices. It is necessary to take this fact to account when dealing with microcircuits for space applications and high energy physics. Main physical reason of radiation-induced failures of spaceship and front end electronic equipment is buidup of interface traps at Si-SiO2 interface in semiconductor transistor structures. The original mechanism of interface trap annealing based on radiation induced charge neutralization (RICN) effect is presented. It is supposed that the positive charge of trapped holes in oxide is transformed through electron capture into a new defect (the AD center). The AD centers act as interface traps. The appearance of the A–D+ state leads to the annihilation of the AD center or annealing of interface trap. The annihilation process can be stimulated by radiation induced or substrate electrons. The competitive between accumulation and annihilation processes leads to saturation of the interface trap buildup. The value of density of interface trap in saturation depends on product of interface trap accumulation rate (Kacc)it and constant KAD which is function of thermal velocity, capture cross-section of AD center, generation rate and electron yield of radiation induced electrons. The extraction of these parameters allows explaining a known experimental data. The alternative mechanism of the interface trap saturation connected with the exhaustion of initial interface trap precursors is considered.

New Fowler-Nordheim Injection, Charge Neutralization, and Gamma Tests on the REM RFT300 RADFET Dosimeter

Through the injection of a Fowler-Nordheim tunnel current or the inversion of oxide fields during irradiation (Radiation-Induced Charge Neutralization), the oxide charge trapped in thick-oxide (300 nm) commercial RADFETs, often called QOT could be erased. Novel trapped-hole and interface characteristics were observed after treatments of this type at high doses. With both erasure techniques, it was possible only to neutralize a fraction of the oxide trapped charge. A non negligible amount of charge and border traps is deemed here to be “intractable”. That adjective an a symbol, QIN, are introduced for the first time in this paper. Later sections discuss the possible impact of these results. The conclusion for dosimetry is that a “reusable RADFET” dosimeter, working up to an unprecedented dose before wearing out, may be a practical possibility.

Extension of the Measurement Range of MOS Dosimeters Using Radiation Induced Charge Neutralization

This work proposes a new measurement technique to extend the dose range of MOS dosimeters. The technique consists on alternating stages of positive oxide charge buildup with stages of radiation induced charge neutralization, maintaining a uniform sensitivity along the whole measurement. The technique was applied with 70 nm MOS dosimeters, extending the dose measurement range from less than a kilogray to more than 675 kGy without showing wear effects. An initial saturation of interface traps creation ensures repeatability in the responses.

The empirical dependence of radiation-induced charge neutralization on negative bias in dosimeters based on the metal-oxide-semiconductor field-effect transistor

The dependence of radiation-induced charge neutralization (RICN) has been studied in metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters. These devices were first exposed to x rays under positive bias and then to further dose increments at a selection of reverse bias levels. A nonlinear empirical trend has been established that is consistent with that identified in the data obtained in this work. Estimates for the reverse bias level corresponding to the maximum rate of RICN have been extracted from the data. These optimum bias levels appear to be independent of the level of initial absorbed dose under positive bias. The established models for threshold voltage change have been considered and indicate a related nonlinear trend for neutralization cross section σN as a function of oxide field. These data are discussed in the context of dose measurement with MOSFETs and within the framework of statistical mechanics associated with neutral traps and their field dependence.

Use of the radiation-induced charge neutralization mechanism to achieve annealing of 0.35 /spl mu/m SRAMs

Irradiation of electronic devices has varying impact on their electrical characteristics, according to the concomitant bias scenario. Under bias, there is a process of continuous degradation; but recovery will occur if subsequent irradiation is performed without bias voltage. This phenomenon, known as "Radiation-Induced Charge Neutralization" (RICN), was studied by us, using individual components (inverters) and complex integrated circuits (0.35 /spl mu/m static random access memories). Our study focused on the effects of irradiation and bias on electronic component response.

The effect of emitter junction bias on the low dose-rate radiation response of bipolar devices

It is shown that emitter-base junction bias is significant for low dose rate irradiation response of npn and pnp bipolar transistors. The effect is more pronounced for pnp transistor. Experimental results are explained in terms of fringing electric field model. The role of fringing field is confirmed by the radiation induced charge neutralization experiment. The experimental results on the effect of emitter junction bias on the elevated temperature high dose rate irradiation of bipolar devices and its application for low dose rate response simulation are discussed.

Qualifying commercial ICs for space total-dose environments

A test protocol based on MIL-STD-883D, Test Method 1019.4, which includes a room-temperature biased anneal following irradiation, is shown to predict device response to low-dose-rate irradiations more accurately than the present standard. Failure dose was measured with three test protocols: with Method 1019.4, with Method 1019.4 plus a room-temperature anneal, and with 0.2 rad(Si)/s irradiations at static and dynamic bias. In comparing the power-supply current (I/sub DD/) of two commercial field-programmable gate arrays (FPGAs), it was found that the failure dose for devices with a high annealing rate increased by a factor of ten times when a room-temperature anneal was included, while devices with a slower annealing rate showed almost a two-times improvement in failure dose. Slower-annealing devices showed a higher failure dose when dynamically biased during low dose-rate irradiations, indicating that radiation-induced charge neutralization accelerated recovery in these devices. Methods of characterizing the hardness of MOS ICs using a test flow that includes room-temperature and elevated-temperature anneals are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Predicting switched-bias response from steady-state irradiations MOS transistors

A novel semiempirical model of radiation-induced charge neutralization is presented. This model is combined with 12 heuristic guidelines derived from studies of oxide- and interface-trap charge ( Delta V/sub ot/ and Delta V/sub it/) buildup and annealing to develop a method to predict MOS switched-bias response from steady-state irradiations, with no free parameters. For n-channel MOS devices, predictions of Delta V/sub ot/, Delta V/sub it/, and mobility degradation differ from experimental values through irradiation by less than 30% in all cases considered. This is demonstrated for gate oxides with widely varying Delta V/sub ot/ and Delta V/sub it/ and for parasitic field oxides. Preliminary results suggest that n-channel MOS Delta V/sub ot/ annealing and Delta V/sub it/ buildup following switched-bias irradiation and through switched-bias annealing also may be predicted with less than 30% error. The p-channel MOS response at high frequencies (>1 kHz) is more difficult to predict. >

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 &amp;lt;−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.