Charge Multiplication Effects Research Articles

Transient‐Current Technique Characterization of Diamond Detector and Proposal of a Diamond Detector with Charge Amplification

Diamond holds promise as a potential candidate for future particle detectors owing to its remarkable electronic, mechanical, and thermal properties. However, a notable limitation is the need for a comprehensive model characterizing intrinsic diamond detectors. To address this, a specialized model integrated into the technology computer‐aided design simulation program is developed. The model's validation is accomplished through its application to the evaluation of an intrinsic diamond detector. Our investigation emphasizes three key attributes: charge carrier mobility, charge carrier lifetime, and the effective charge density within the bulk material. These attributes are carefully assessed using the transient current technique. Furthermore, our model serves as a valuable tool in the analysis of the quality of an high‐pressure high‐temperature diamond crystal and in the optimization of a diamond detector's design, exploiting the charge multiplication effect. This comprehensive methodology advances our grasp of diamond detector behavior and facilitates the development of even more sophisticated devices.

Quantum Efficiency Gain in 2D Perovskite Photo and X‐Ray Detectors

AbstractThe perovskite polycrystalline thin film detector fabricated by solution method is a promising low‐cost, scalable technology for radiation imaging, but its thin volume limits the sensing efficiency for high‐energy X‐ray photons. This work reports 2D perovskite thin film photo‐diodes with a detection gain when sensing visible and X‐ray photons. Detailed power and temperature‐dependent device characterizations reveal a charge multiplication effect to be responsible for the observed high gain. This is caused by a disparity in electron and hole transport, where electron transport is retarded by a trap/de‐trap process via shallow trap states, whereas the hole transport is fast enough to produce a photoconductive gain in satisfying the charge neutrality. The 2D perovskite made with butylamine spacers is also found to exhibit a larger efficiency gain than those made with phenylethylamines because of the higher likelihood of forming shallow traps in the former. The thin film diodes feature a high temporal response over 1 MHz due to the fast charge collection across a thin volume, and the discovery provides device physics mechanisms in connection to material structure‐function relationship for future optoelectronics design that can boost the efficiency of X‐ray sensing and dim light detection.

Ultrahigh dose rate pencil beam scanning proton dosimetry using ion chambers and a calorimeter in support of first in‐human FLASH clinical trial

PurposeTo provide ultrahigh dose rate (UHDR) pencil beam scanning (PBS) proton dosimetry comparison of clinically used plane‐parallel ion chambers, PTW (Physikalisch‐Technische Werkstaetten) Advanced Markus and IBA (Ion Beam Application) PPC05, with a proton graphite calorimeter in a support of first in‐human proton FLASH clinical trial.MethodsAbsolute dose measurement intercomparison of the plane‐parallel plate ion chambers and the proton graphite calorimeter was performed at 5‐cm water‐equivalent depth using rectangular 250‐MeV single‐layer treatment plans designed for the first in‐human FLASH clinical trial. The dose rate for each field was designed to remain above 60 Gy/s. The ion recombination effects of the plane‐parallel plate ion chambers at various bias voltages were also investigated in the range of dose rates between 5 and 60 Gy/s. Two independent model‐based extrapolation methods were used to calculate the ion recombination correction factors ks to compare with the two‐voltage technique from most widely used clinical protocols.ResultsThe mean measured dose to water with the proton graphite calorimeter across all the predefined fields is 7.702 ± 0.037 Gy. The average ratio over the predefined fields of the PTW Advanced Markus chamber dose to the calorimeter reference dose is 1.002 ± 0.007, whereas the IBA PPC05 chamber shows ∼3% higher reading of 1.033 ± 0.007. The relative differences in the ks values determined from between the linear and quadratic extrapolation methods and the two‐voltage technique for the PTW Advanced Markus chamber are not statistically significant, and the trends of dose rate dependence are similar. The IBA PPC05 shows a flat response in terms of ion recombination effects based on the ks values calculated using the two‐voltage technique. Differences in ks values for the PPC05 between the two‐voltage technique and other model‐based extrapolation methods are not statistically significant at FLASH dose rates. Some of the ks values for the PPC05 that were extrapolated from the three‐voltage linear method and the semiempirical model were reported less than unity possibly due to the charge multiplication effect, which was negligible compared to the volume recombination effect in FLASH dose rates.ConclusionsThe absolute dose measurements of both PTW Advanced Markus and IBA PPC05 chambers are in a good agreement with the National Physical Laboratory graphite calorimeter reference dose considering overall uncertainties. Both ion chambers also demonstrate good reproducibility as well as stability as reference dosimeters in UHDR PBS proton radiotherapy. The dose rate dependency of the ion recombination effects of both ion chambers in cyclotron generated PBS proton beams is acceptable and therefore, both chambers are suitable to use in clinical practice for the range of dose rates between 5 and 60 Gy/s.

A Modified 3D-Trench Pixel Detector: Proof of Concept by TCAD Simulations

A design modification to an existing 3D-trenched pixel detector is proposed, aimed at an improved fabrication yield. The device concept is studied and its performance is evaluated by TCAD simulations, in comparison to the existing one. Although the modified design features a less uniform electric field distribution, it is still expected to yield a very good timing performance and high radiation tolerance, also exploiting charge multiplication effects.

Determination of ion recombination and polarity effects for the PTW Advanced Markus ionization chamber in synchrotron based scanned proton and carbon ion beams

The aim of this work was the investigation of the ion recombination and polarity factors (ksat ad kpol) for a PTW Advanced Markus ionization chamber exposed to proton and carbon ion beams at the Centro Nazionale di Adroterapia Oncologica. Measurements with protons were specifically dedicated for ocular treatments, in the low energy range and for small, collimated scanning fields. For both protons and carbon ions, several measurements were performed by delivering a 2D single energy layer of 3x3 cm2 and homogeneous, biologically-optimized SOBPs. Data were collected at different depths in water, by varying the voltage values of the ionization chamber and for two different dose rates (the nominal one and one reduced to 20% of it). The ksat-values were determined from extrapolation of the saturation curves. Furthermore kpol-values were calculated using the recommendations from the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)-398 Code of Practice.Results showed that the Advanced Markus performs optimally in this clinical scenario characterized by small treatment volumes and high dose gradients although for both particle types, but particularly for carbon ions, a charge multiplication effect up to 1.7% occurs at voltage higher than 150 V.For protons, both the ion recombination and polarity corrections were always smaller than 0.3%, for all the analysed cases and adopted dose rates, so not affecting the dosimetric measurements for clinical routine. For carbon ions the polarity effect can be neglected while ion recombination has to be carefully calculated and cannot be neglected since corrections even higher than 1% can be found, especially at high LET measuring points.

Correction of the measured current of a small-gap plane-parallel ionization chamber in proton beams in the presence of charge multiplication

PurposeThe aims of this work are to study the response of a small-gap plane-parallel ionization chamber in the presence of charge multiplication and suggest an experimental method to determine the product of the recombination correction factor (ks) and the charge multiplication correction factor (kCM) in order to investigate the latter. MethodsExperimental data were acquired in scanned proton beams and in a Cobalt-60 beam. Measurements were carried out using an IBA PPC05 chambers of which the electrode gap is 0.6mm. The study is based on the determination of Jaffé plots by operating the chambers at different voltages. Experimental results are compared to theoretical equations describing initial and volume recombination as well as charge multiplication for continuous and pulsed beams. ResultsResults obtained in protons and Cobalt-60 with the same PPC05 chamber indicate that the charge multiplication effect is independent of the beam quality, while results obtained in different proton beams with two different PPC05 chambers show that the charge multiplication effect is chamber dependent. ConclusionsThe approach to be taken when using a small-gap plane-parallel ionization chamber with a high voltage (e.g. 300V or 500V) for reference dosimetry in scanned proton beams depends on which correction factors were applied to the chamber response during its calibration in terms of absorbed dose to water:-if ks and kCM are applied during the calibration, the user can use a linear extrapolation method (e.g. two-voltage method or 3VL-method) to determine the product of ks and kCM in the user beam.-if ks and kCM are not applied during the calibration: the user can neglect kCM and determine ks in the user beams using a linear interpolation of the chamber response.In both cases, it is recommended to use the ionization chamber at the same operating voltage used during its ND,w-calibration.Another solution consists of operating the PPC05 chamber at a lower voltage (e.g. 50V) with larger ks and smaller kCM and determining the product of both factors with higher accuracy using a linear extrapolation method.

Characterization of FBK small-pitch 3D diodes after neutron irradiation up to 3.5 × 1016 neq cm−2

We report on the characterization by a position resolved laser system of small-pitch 3D diodes irradiated with neutrons up to an extremely high fluence of 3.5 × 1016 neq cm−2. We show that very high values of signal efficiency are obtained, in good agreement with the geometrical expectation based on the small values of the inter-electrode spacings, and also boosted by charge multiplication effects at high voltage. These results confirm the very high radiation tolerance of small-pitch 3D sensors well beyond the maximum fluences expected at the High Luminosity LHC.

129. Recombination effects in parallel-plates ionization chambers under clinical continuous active scanning proton beams

PurposeSeveral factors can influence the response of an ionization chamber (IC) when exposed to radiation. One of these is the ion recombination. It depends mainly on dose rate (volumetric recombination, Vrec) and ionization density (initial recombination, Irec). This work aimed to determine the recombination correction factor (Ks) for parallel-plates (PP) ICs irradiated under continuous pencil beam scanning proton beams. MethodsPPICs were exposed to clinical proton beams produced by an isochronous cyclotron (Proteus®PLUS-Iba). To compensate for fluctuations of the beam two PPICs were set face-to-face, one used as monitor and the second was the PPIC under study, as explained in [1]. To separate Vrec and Irec, measurements were performed at different dose-rates (minimum cyclotron current 75 nA, maximum 300 nA) and different voltage (20 V–500 V). Ks was obtained as the ratio between the saturation current (Isat) and the ionization current (I) measured at the operating voltage (Ks=Isat/I) [1]. This was carried-out for three scenarios: (a) single 10 × 10 cm2 unmodulated 100 MeV layer; (b) single 10 × 10 cm2 unmodulated 226 MeV layer; (c) modulated box-like field (range 15 cm-modulation 10 cm). A theoretical model is under investigation to be compared to Ks-values determined with the two-voltage method [2] for continuous beam. Only results obtained using an PPC05 IC (Iba-Dosimetry) are reported. ResultsAll scenarios show similar results (Figure). At high voltages, data has an exponential trend, highlighting the presence of charge multiplication effects (CME). This should be due to the small gap (0.6 mm) between electrodes. At low voltages, there is a rather linear relation between 1/I and 1/V2. Using the two-voltage method, at +300 V, a Ks-value of 1.001 is found in all scenarios. Due to CME this value could be overestimated. ConclusionsAlthough the proton beam used can be considered as continuous, the variation of Ks against 1/V2 is not linear due to CME, so the two-voltage method use might be unsuitable. Further investigations are currently made to decouple recombination effect from CME and derive a model for accurately determine Ks.▪

Charge multiplication effect in thin diamond films

Herein, we report on the enhanced sensitivity for the detection of charged particles in single crystal chemical vapour deposition (scCVD) diamond radiation detectors. The experimental results demonstrate charge multiplication in thin planar diamond membrane detectors, upon impact of 18 MeV O ions, under high electric field conditions. Avalanche multiplication is widely exploited in devices such as avalanche photo diodes, but has never before been reproducibly observed in intrinsic CVD diamond. Because enhanced sensitivity for charged particle detection is obtained for short charge drift lengths without dark counts, this effect could be further exploited in the development of sensors based on avalanche multiplication and radiation detectors with extreme radiation hardness.

Characterization of thin irradiated epitaxial silicon sensors for the CMS phase II pixel upgrade

The high-luminosity upgrade of the Large Hadron Collider foreseen for 2023 resulted on the decision to replace the tracker system of the CMS experiment. The innermost layer of the new pixel detector will experience fluences in the order of ϕeq ≈ 1016 cm−2 and a dose of ≈ 5 MGy after an integrated luminosity of 3000 fb−1. Several materials and designs are under investigation in order to build a detector that can withstand such high fluences. Thin planar silicon sensors are good candidates to achieve this goal since the degradation of the signal produced by traversing particles is less severe than for thicker devices. A study has been carried out in order to characterize highly irradiated planar epitaxial silicon sensors with an active thickness of 100 μm. The investigation includes pad diodes and strip detectors irradiated up to a fluence of ϕeq = 1.3 × 1016 cm−2, and 3 × 1015 cm−2, respectively. The electrical properties of diodes have been characterized using laboratory measurements, while measurements have been carried out at the DESY II test beam facility to characterize the charge collection of the strip detectors. A beam telescope has been used to determine precisely the impact position of beam particles on the sensor. This allows the unbiased extraction of the charge deposited in the strip sensor and good identification of the noise. In this paper, the results obtained for p-bulk sensors are shown. The charge collection efficiency of the strip sensors is 90% at 1000 V after a fluence of ϕeq = 3 × 1015 cm−2. The irradiated diodes show charge multiplication effects. The impact of the threshold applied to a detector on its efficiency is also discussed.

Technology developments and first measurements of Low Gain Avalanche Detectors (LGAD) for high energy physics applications

This paper introduces a new concept of silicon radiation detector with intrinsic multiplication of the charge, called Low Gain Avalanche Detector (LGAD). These new devices are based on the standard Avalanche Photo Diodes (APD) normally used for optical and X-ray detection applications. The main differences to standard APD detectors are the low gain requested to detect high energy charged particles, and the possibility to have fine segmentation pitches: this allows fabrication of microstrip or pixel devices which do not suffer from the limitations normally found [1] in avalanche detectors. In addition, a moderate multiplication value will allow the fabrication of thinner devices with the same output signal of standard thick substrates.The investigation of these detectors provides important indications on the ability of such modified electrode geometry to control and optimize the charge multiplication effect, in order to fully recover the collection efficiency of heavily irradiated silicon detectors, at reasonable bias voltage, compatible with the voltage feed limitation of the CERN High Luminosity Large Hadron Collider (HL-LHC) experiments [2]. For instance, the inner most pixel detector layers of the ATLAS tracker will be exposed to fluences up to 2×10161MeVneq/cm2, while for the inner strip detector region fluences of 1×1015neq/cm2 are expected.The gain implemented in the non-irradiated devices must retain some effect also after irradiation, with a higher multiplication factor with respect to standard structures, in order to be used in harsh environments such those expected at collider experiments.

Development of radiation tolerant silicon sensors

Within the CERN RD50 Collaboration, a massive R&D programme is underway across experimental boundaries to develop silicon sensors with sufficient radiation tolerance. One research topic is to gain a deeper understanding of the connection between the macroscopic sensor properties such as radiation-induced increase of leakage current, doping concentration and trapping, and the microscopic properties at the defect level. RD50 also studies sensors made from p-type silicon bulk, which have a superior radiation hardness as they collect electrons instead of holes, exploiting the lower trapping probability of the electrons due to their higher mobility. Simulations have become important to predict the performance of silicon sensors at high fluences. They can be a useful tool to explore the large parameter space of strip sensor geometries and help to explain the charge multiplication effect occuring in sensors at high radiation levels. Charge multiplication plays an important role in sensors irradiated to high fluences and is investigated in RD50. Several studies are ongoing to exploit the effect for future silicon sensors. The latest results of the microscopic studies, the simulation activities, the performance of heavily irradiated strip sensors and the investigations on charge multiplication are presented.

Silicon for High-Luminosity Tracking Detectors -Recent RD50 Results

In order to harvest the maximum physics potential of the CERN Large Hadron Collider (LHC), it is foreseen to significantly increase the LHC luminosity by upgrading the LHC towards the HL-LHC (High Luminosity LHC) [1] . Especially the final upgrade (Phase-II Upgrade) foreseen beyond 2020 will mean unprecedented radiation levels. Due to the radiation damage limitations of the silicon sensors presently used, the physics experiments will require new tracking detectors for HL-LHC operation. All-silicon central trackers are being studied in ATLAS, CMS and LHCb, with extremely radiation hard silicon sensors to be used for the innermost layers. Within the CERN RD50 Collaboration, a massive R&D programme is underway across experimental boundaries to develop silicon sensors with sufficient radiation tolerance. One research topic is to gain a deeper understanding of the connection between the macroscopic sensor properties such as radiation-induced increase of leakage current, doping concentration and trapping, and the microscopic properties at the defect level. A further area of activity is the development of advanced sensor types like 3D silicon detectors designed for the extreme radiation levels expected for the vertexing layers at the HL-LHC. Results from irradiation with a mix of different particle types as expected for the sLHC are also given. Recent observations of charge multiplication effects in heavily irradiated detectors at very high bias voltages point towards a new way to achieve sizeable signals after high fluences. Results for several detector technologies and silicon materials at radiation levels corresponding to HL-LHC fluences are presented in this article, demonstrating the availabilty of silicon detectors with sufficient radiation hardness for the different radii of tracking systems in the LHC detector upgrades.

Accelerated annealing of n+-p strip detectors irradiated with pions

Charge collection measurements with silicon detectors with implanted n-type readout strips in p-type silicon bulk (n+-p) are presented. Detectors were irradiated with 191 MeV pions at the Paul Scherrer Institute (PSI) in Villigen in Switzerland. Signals induced by electrons from 90Sr source were measured with SCT128 chip. Collected charge and detector current were measured after several annealing steps summing up to over 10000 minutes at 60°C. It was observed that irradiation of these detectors with pions results in only ∼ 30% of the increase of Vfd seen after irradiation with neutrons to the same NIEL equivalent fluence. Charge multiplication effects in pion irradiated detectors were seen only after long accelerated annealing time. Both effects are consistent with smaller space-charge introduction rates after irradiation with charged hadrons, characteristic for oxygenated detector material. It was confirmed that, at sufficient bias voltage, reverse annealing after pion irradiation does not represent a problem for application of these detectors in trackers at upgraded LHC.

Beam Test Measurements With Planar and 3D Silicon Strip Detectors Irradiated to sLHC Fluences

The planned luminosity upgrade of the CERN LHC to the super LHC (sLHC) requires investigation of new radiation hard tracking detectors. Compared to the LHC, tracking detectors must withstand a 5–10 times higher radiation fluence. Promising radiation hard options are planar silicon detectors with n-side readout and silicon detectors in 3D technology, where columnar electrodes are etched into the silicon substrate. This article presents beam test measurements performed with planar and 3D n-in-p silicon strip detectors. The detectors were irradiated to different fluences, where the maximum fluence was <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$3\times 10^{15}$</tex></formula> 1 MeV neutron equivalent particles per square centimeter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$({\rm n}_{\rm eq}/{\rm cm}^{2})$</tex></formula> for the planar detectors and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${2\times 10^{15}~{\rm n}_{\rm eq}/{\rm cm}^{2}}$</tex></formula> for the 3D detectors. In addition to signal measurements, charge sharing and resolution of both detector technologies are compared. An increased signal from the irradiated 3D detectors at high bias voltages compared to the signal from the unirradiated detector indicates that charge multiplication effects occur in the 3D detectors. At a bias voltage of 260 V, the 3D detector irradiated to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${2\times 10^{15}~{\rm n}_{\rm eq}/{\rm cm}^{2}}$</tex> </formula> yields a signal almost twice as high as the signal of the unirradiated detector. Only 30% of the signal of an unirradiated detector could be measured with the planar detector irradiated to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${3\times 10^{15}~{\rm n}_{\rm eq}/{\rm cm}^{2}}$</tex></formula> at a bias voltage of 600 V, which was the highest bias voltage applied to this sensor.

Simulation of new p-type strip detectors with trench to enhance the charge multiplication effect in the n-type electrodes

This paper shows the simulation results of new p-type strip detectors with trench electrodes to enhance the charge multiplication effect in the irradiated detector. The new design includes baby microstrip detectors (area=1 cm2) with a strip pitch of 80 μm and p-stop isolation structures. The strip has a 5 μm-wide trench along all its length, filled and doped with polysilicon to create a deep N+contact into the material bulk. The trench depth can be varied in order to study the influence of the electric field on the charge multiplication effect in heavily irradiated samples. Some alternative designs have also been studied to establish a comparison between various structures using different technologies. Simulation reproduce the electrical behaviour under different irradiation conditions, taking into account the damage accumulated after irradiation with neutrons and protons with several fluence values. The investigation of these effects provides important indications on the ability of this modified electrode geometry to control and optimise the charge multiplication effect, in order to fully recover the collection efficiency of heavily irradiated microstrip detectors, at reasonable bias voltage compatible with the voltage feed limitation of the CERN SLHC experiments.

Silicon detectors for the sLHC

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages.

Charge collection studies of proton-irradiated n- and p-type epitaxial silicon detectors

Proton-irradiated epitaxial pad diodes of 75, 100 and 150 μ m thickness and different oxygen concentrations were studied as an option to withstand the extreme radiation environment in the innermost tracking region of the future Super-LHC. With a new TCT setup using red laser light, time-resolved current signals could be measured in 150 μ m thin diodes. Thus the charge correction method (CCM) could be used to extract the effective trapping times. Similar results compared to previously investigated materials were obtained if the standard model of trapping is assumed, which is based on a constant trapping time at each fluence and neglects detrapping and charge multiplication. Charge collection efficiency (CCE) measured with 5.8 MeV α -particles showed an increase for decreasing thickness, but no dependence on impurity concentration was seen. CCE simulations based on the effective trapping time constants determined with the CCM resulted in systematically lower values than the measurements. This is the case for the CCE of both α -particles , red and infrared laser light. To account for this, possible modifications of the trapping model including voltage- or field-dependent trapping times will be discussed. Moreover, at high fluences and voltages anomalously high CCE > 1 was observed, which indicates charge multiplication effects.

Saturation current and collection efficiency for ionization chambers in pulsed beams.

Saturation currents and collection efficiencies in ionization chambers exposed to pulsed megavoltage photon and electron beams are determined assuming a linear relationship between 1/I and 1/V in the extreme near-saturation region, with I and V the chamber current and polarizing voltage, respectively. Careful measurements of chamber current against polarizing voltage in the extreme near-saturation region reveal a current rising faster than that predicted by the linear relationship. This excess current combined with conventional "two-voltage" technique for determination of collection efficiency may result in an up to 0.7% overestimate of the saturation current for standard radiation field sizes of 10X10 cm2. The measured excess current is attributed to charge multiplication in the chamber air volume and to radiation-induced conductivity in the stem of the chamber (stem effect). These effects may be accounted for by an exponential term used in conjunction with Boag's equation for collection efficiency in pulsed beams. The semiempirical model follows the experimental data well and accounts for both the charge recombination as well as for the charge multiplication effects and the chamber stem effect.

Experimental and simulation study of the effects of cosmic particles on CMOS/SOS RAMs

The existence of a charge multiplication effect in CMOS/SOS RAM circuits, as reported by J. Rollins (1987), is confirmed. Shorter channel lengths and higher power supply voltages caused the ratio, M, of upset charge to deposited charge to increase. As a result of this multiplication factor, actual devices are more likely to upset than expected from an analysis of only the collected charge. A mixed-mode simulator was used to model the charge collection process. The results showed that the M factor is a very fluid number which is dependent on minority carrier lifetime, drain voltage, and the switching dynamics of the cell in addition to the dependence on mobility ratio and channel length reported by Rollins. Parasitic bipolar gain at high injection levels appears to be the primary mechanism allowing collected charge to be greater than deposited charge. The simulator and experimental data show that, as floating body static memory transistors are down scaled, the particle energy needed to upset the cell is reduced because of the enhanced parasitic bipolar gain effect as well as a reduction in the node capacitance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>