Using 3D TCAD Simulation to Study Charge Collection of a p-n Junction in a 0.18μm Bulk Process

Single event transient of a real p-n junction in a 0.18μm bulk process is studied by 3D TCAD simulation. The impact of voltage, temperature, substrate concentration, and LET on SET is studied. Our simulation results demonstrate that biases in the range 1.62 to 1.98V influence DSET current shape greatly and total collected charge weakly. Peak current and charge collection within 2ns decreases as temperature increases,and temperature has a stronger influence on SET currents than on total charge. Typical variation of substrate concentration in modern VDSM processes has a negligible effect on SEEs. Both peak current and total collection charge increases as LET increases.

The modulation effect of substrate doping on multi-node charge collection and single-event transient propagation in 90-nm bulk complementary metal-oxide semiconductor technology

Variation of substrate background doping will affect the charge collection of active and passive MOSFETs in complementary metal-oxide semiconductor （CMOS） technologies, which are significant for charge sharing, thus affecting the propagated single event transient pulsewidths in circuits. The trends of charge collected by the drain of a positive channel metal-oxide semiconductor （PMOS） and an N metal-oxide semiconductor （NMOS） are opposite as the substrate doping increases. The PMOS source will inject carriers after strike and the amount of charge injected will irlcrease as the substrate doping increases, whereas the source of the NMOS will mainly collect carriers and the source of the NMOS can also inject electrons when the substrate doping is light enough. Additionally, it indicates that substrate doping mainly affects the bipolar amplification component of a single-event transient current, and has little effect on the drift and diffusion. The change in substrate doping has a much greater effect on PMOS than on NMOS.

Effects of NPB anode buffer layer on charge collection in ZnO/MEH-PPV hybrid solar cells

We investigate the effects of （N,N’-diphenyl）-N,N’-bis（1-naphthyl）-1,1’-biphenyl-4,4’-diamine （NPB） buffer layers on charge collection in inverted ZnO/MEH-PPV hybrid devices. The insertion of a 3-nm NPB thin layer enhances the efficiency of charge collection by improving charge transport and reducing the interface energy barrier, resulting in better device performances. S-shaped light J–V curve appears when the thickness of the NPB layer reaches 25 nm, which is induced by the inefficient charge extraction from MEH-PPV to Ag. Capacitance–voltage measurements are performed to further investigate the influence of the NPB layer on charge collection from both simulations and experiments.

Defect-rich spinel ferrites with improved charge collection properties for efficient solar water splitting

Spinel zinc ferrite(ZnFe_(2)O_(4),ZFO)is a potential photoanode material for photoelectrochemical(PEC)water splitting because of its ideal bandgap(1.9–2.1 eV)and superior chemical stability in aqueous solutions.However,the low charge collection efficiency significantly hinders the improvement in PEC activity.Herein,we report an ultrafast and effective flame activation route to enhance the charge collection properties of ZFO.First,high-temperature flame(>1300℃)facilitated surface and grain boundary diffusions,increasing the grain size and connectivity of the ZFO nanoparticles.Second,the reducing atmosphere of the flame enabled the formation of surface defects(oxygen vacancy and Fe^(2+)),thereby increasing the charge carrier density and surface adsorption sites.Significantly,these two factors promoted charge transport and transfer kinetics,resulting in a 10-fold increase in the photocurrent density over the unactivated ZFO.Furthermore,we deposited a thin Al_(2)O_(3)overlayer to passivate the ZFO surface and then the NiFeOx oxygen evolution catalyst(OEC)to expedite hole injection into the electrolyte.This surface passivation and OEC deposition led to a remarkable photocurrent density of~1 mA/cm^(2)at 1.23 V versus the reversible hydrogen electrode,which is the highest value among all reported ZFO photoanodes.Notably,the NiFeOx/Al_(2)O_(3)/F-ZFO photoanode achieved excellent photocurrent stability over 55 h(96%retention)and superior faradaic efficiency(FE>94%).Our flame activation method is also effective in improving the photocurrent densities of other spinel ferrites:CuFe_(2)O_(4)(93 times),MgFe_(2)O_(4)(16 times),and NiFe_(2)O_(4)(12 times).

A new semiconductor-based SERS substrate with enhanced charge collection and improved carrier separation: CuO/TiO_(2) p-n heterojunction

In this paper, CuO/TiO_(2) p-n heterojunction was developed as a new surface enhanced Raman scattering(SERS) substrate to magnify Raman signal of 4-mercaptobenzoic acid(4-MBA) molecule. In the heterojunction-molecule system, CuO as an “electron capsule” can not only offer more electrons to inject into the surface state energy level of TiO_(2) and consequently bring additional charge transfer, but also improve photogenerated carrier separation efficiency itself due to strong interfacial coupling in the interface of heterojunction, which together boost SERS performance of the heterojunction substrate. As expected,owing to the enhanced charge collection capacity and the improvement of photogenerated carrier separation efficiency derived from internal electric field and strong interface coupling provided in the interface of heterojunction, this substrate exhibits excellent SERS detection sensitivity towards 4-MBA, with a detection limit as low as 1 × 10^(-10)mol/L and an enhancement factor of 8.87 × 10~6.

Proton-induced current transient in SiGe HBT and charge collection model based on Monte Carlo simulation

The study presents an investigation into the proton-induced current transient in a silicon-germanium heterojunction bipolar transistor(SiGe HBT).The temporal information of the proton-induced current transients is first measured and then compared with results from heavy ion microbeam experiment.Additionally,a model for proton-induced charge collection based on Geant4 Monte Carlo simulation tools is constructed by using the information from heavy ion experiment and 3D TCAD simulation.The results obtained by the validated model exhibit good consistency with the proton experiment.

Charge collection of single event effects at Bragg's peak

Using Geant4 Monte Carlo code and Technology Computer-Aided Design(TCAD) simulation,energy deposition and charge collection of single event effects(SEE) are studied,which are induced by low-energy protons and α particles in small feature size devices.We analyzed charge collection of SEE especially at Bragg's peak and obtained two types of deposited energy distributions of protons and α particles at different incident energies.The two components of the total charge collected are quantified,which are due to drift current of the space charge region and current in the funnel region separately.Results explain the high soft error rate in experiments of low energy proton.

Significant Enhancement in Built-in Potential and Charge Carrier Collection of Organic Solar Cells using 4-（5-hexylthiophene-2-yl）-2,6-bis（5- trifluoromethyl）thiophen-2-yl）pyridine as a Cathode Buffer Layer

An electron transporting material of TFTTP （4-（5-hexylthiophene-2-yl）-2,6-bis（5-trifluoromethyl）thiophen-2-yl）pyridine） was investigated as a cathode buffer layer to enhance the power efficiency of organic solar cells （OSCs） based on subphthalocyanine and C60. The overall power conversion efficiency was increased by a factor of 1.31 by inserting the TFTTP interfacial layer between the active layer and metallic cathode. The inner mechanism responsible for the performance enhancement of OSCs was systematically studied with the simulation of dark diode behavior and optical field distribution inside the devices as well as the characterization of device photocurrent. The results showed that the TFTTP layer could significantly increase the built-in potential in the devices, leading to the enhanced dissociation of charge transfer excitons. In addition, by using TFTTP as the buffer layer, a better Ohmic contact at C60/metal interface was formed, facilitating more efficient free charge carrier collection.

The dual role of multiple-transistor charge sharing collection in single-event transients

As technologies scale down in size, multiple-transistors being affected by a single ion has become a universal phenomenon, and some new effects are present in single event transients （SETs） due to the charge sharing collection of the adjacent multiple-transistors. In this paper, not only the off-state p-channel metal–oxide semiconductor field-effect transistor （PMOS FET）, but also the on-state PMOS is struck by a heavy-ion in the two-transistor inverter chain, due to the charge sharing collection and the electrical interaction. The SET induced by striking the off-state PMOS is efficiently mitigated by the pulse quenching effect, but the SET induced by striking the on-state PMOS becomes dominant. It is indicated in this study that in the advanced technologies, the SET will no longer just be induced by an ion striking the off-state transistor, and the SET sensitive region will no longer just surround the off-state transistor either, as it is in the older technologies. We also discuss this issue in a three-transistor inverter in depth, and the study illustrates that the three-transistor inverter is still a better replacement for spaceborne integrated circuit design in advanced technologies.

Heavy ion energy influence on multiple-cell upsets in small sensitive volumes:from standard to high energies

The 28 nm process has a high cost-performance ratio and has gradually become the standard for the field of radiation-hardened devices.However,owing to the minimum physical gate length of only 35 nm,the physical area of a standard 6T SRAM unit is approximately 0.16μm^(2),resulting in a significant enhancement of multi-cell charge-sharing effects.Multiple-cell upsets(MCUs)have become the primary physical mechanism behind single-event upsets(SEUs)in advanced nanometer node devices.The range of ionization track effects increases with higher ion energies,and spacecraft in orbit primarily experience SEUs caused by high-energy ions.However,ground accelerator experiments have mainly obtained low-energy ion irradiation data.Therefore,the impact of ion energy on the SEU cross section,charge collection mechanisms,and MCU patterns and quantities in advanced nanometer devices remains unclear.In this study,based on the experimental platform of the Heavy Ion Research Facility in Lanzhou,low-and high-energy heavy-ion beams were used to study the SEUs of 28 nm SRAM devices.The influence of ion energy on the charge collection processes of small-sensitive-volume devices,MCU patterns,and upset cross sections was obtained,and the applicable range of the inverse cosine law was clarified.The findings of this study are an important guide for the accurate evaluation of SEUs in advanced nanometer devices and for the development of radiation-hardening techniques.

Low-noise and low-power pixel sensor chip for gas pixel detectors

Topmetal-M2 is a large-area pixel sensor chip fabricated using the GSMC 130 nm CMOS process in 2021.The pixel array of Topmetal-M2 consists of pixels of 400 rows×512 columns with a pixel pitch of 45μm×45μm.The array is divided into 16 subarrays,with pixels of 400 rows×32 columns per subarray.Each pixel incorporates two charge sensors:a diode sensor and a Topmetal sensor.The in-pixel circuit primarily consists of a charge-sensitive amplifier for energy measurements,a discriminator with a peak-holding circuit,and a time-to-amplitude converter for time-of-arrival measurements.The pixel of Topmetal-M2 has a charge input range of~0-3 k e-,a voltage output range of~0-180 mV,and a charge-voltage conversion gain of~59.56μV∕e-.The average equivalent noise charge of Topmetal-M2,which includes the readout electronic system noise,is~43.45 e-.In the scanning mode,the time resolution of Topmetal-M2 is 1 LSB=1.25μs,and the precision is^()7.41μs.At an operating voltage of 1.5 V,Topmetal-M2 has a power consumption of~49 mW∕cm~2.In this article,we provide a comprehensive overview of the chip architecture,pixel working principles,and functional behavior of Topmetal-M2.Furthermore,we present the results of preliminary tests conducted on Topmetal-M2,namely,alpha-particle and soft X-ray tests.

Influence of sub-bandgap illumination on space charge distribution in CdZnTe detector

The space charge accumulation in CdZnTe crystals seriously affects the performance of high-flux pulse detectors.The influence of sub-bandgap illumination on the space charge distribution and device performance in CdZnTe crystals were studied theoretically by Silvaco TCAD software simulation.The sub-bandgap illumination with a wavelength of 890 nm and intensity of 8×10−8 W/cm2 were used in the simulation to explore the space charge distribution and internal electric field distribution in CdZnTe crystals.The simulation results show that the deep level occupation faction is manipulated by the sub-bandgap illumination,thus space charge concentration can be reduced under the bias voltage of 500 V.A flat electric field distribution is obtained,which significantly improves the charge collection efficiency of the CdZnTe detector.Meanwhile,premised on the high resistivity of CdZnTe crystal,the space charge concentration in the crystal can be further reduced with the wavelength of 850 nm and intensity of 1×10−7 W/cm2 illumination.The electric field distribution is flatter and the carrier collection efficiency of the device can be improved more effectively.

Burst pulses for positive corona discharges in atmospheric air:the collective movement of charged species

Positive corona burst pulses are an unstable pulse mode.They appear in a small range of the onset stage,and their current pulses result from the collective movement of charged species.This paper focused on the connections between these pulses and the collective movement of charged species.The movement of species is divided into four parts with respect to time:the(1)initial growth of species,(2)formation and development of the streamer region and negative ion sheath,(3)dead time(the time interval between the pulses),and(4)rapid re-growth of species.The movement of the species in the four parts and the correspondence with the current pulse were analyzed.The numerical results indicated the following:the rapid rising of the species matched the rising edge of the pulses,the streamer region,and negative ion sheath appeared in the falling edge of the primary pulse,and the rapid re-growth of species matched the re-ignition of the pulses.The results were in qualitative agreement with deductions and experimental observations in the literature.

8-nm narrowband photodetection in diamonds

Spectrally-selective photodetection plays a crucial role in various applications,including target imaging and environmental monitoring.Traditional deep-ultraviolet(DUV)narrowband photodetection systems consist of broadband photodetectors and filters,which complicates the architecture and constrains imaging quality.Here,we introduce an electronic-grade diamond single-crystal photodetector exhibiting an exceptionally narrow spectral response in the DUV range with a full width at half maximum of 8 nm.By examining diamond photodetectors with varying dislocation densities,we propose that mitigating the defect-induced trapping effect to achieve charge collection narrowing,assisted by free exciton radiative recombination,is an effective strategy for narrowband photodetection.The superior performance of this device is evidenced through the imaging of DUV light sources,showcasing its capability to differentiate between distinct light sources and monitor human-safe sterilization systems.Our findings underscore the promising potential applications of electronicgrade diamond in narrowband photodetection and offer a valuable technique for identifying electronic-grade diamond.

Multiple Node Upset in SEU Hardened Storage Cells

We study the problem of multiple node upset （MNU） using three-dimensional device simulation. The results show the transient floating node and charge lateral diffusion are the key reasons for MNU. We compare the MNU with multiple bit upset （MBU）,and find that their characteristics are different. Methods to avoid MNU are also discussed.

Estimation of pulsed laser-induced single event transient in a partially depleted silicon-on-insulator 0.18-μm MOSFET

In this paper, we investigate the single event transient （SET） occurring in partially depleted silicon-on-insulator （PDSOI） metal-oxide-semiconductor （MOS） devices irradiated by pulsed laser beams. Transient signal characteristics of a 0.18-p.m single MOS device, such as SET pulse width, pulse maximum, and collected charge, are measured and an- alyzed at wafer level. We analyze in detail the influences of supply voltage and pulse energy on the SET characteristics of the device under test （DUT）. The dependences of SET characteristics on drain-induced barrier lowering （DIBL） and the parasitic bipolar junction transistor （PBJT） are also discussed. These results provide a guide for radiation-hardened deep sub-micrometer PDSOI technology for space electronics applications.

Recovery of single event upset in advanced complementary metal-oxide semiconductor static random access memory cells

Using computer-aided design three-dimensional （3D） simulation technology, the recovery mechanism of single event upset and the effects of spacing and hit angle on the recovery are studied. It is found that the multi-node charge collection plays a key role in recovery and shielding the charge sharing by adding guard rings. It cannot exhibit the recovery effect. It is also indicated that the upset linear energy transfer （LET） threshold is kept constant while the recovery LET threshold increases as the spacing increases. Additionally, the effect of incident angle on recovery is analysed and it is shown that a larger angle can bring about a stronger charge sharing effect, thus strengthening the recovery ability.

The supply voltage scaled dependency of the recovery of single event upset in advanced complementary metal-oxide-semiconductor static random-access memory cells

Using computer-aided design three-dimensional simulation technology,the supply voltage scaled dependency of the recovery of single event upset and charge collection in static random-access memory cells are investigated.It reveals that the recovery linear energy transfer threshold decreases with the supply voltage reducing,which is quite attractive for dynamic voltage scaling and subthreshold circuit radiation-hardened design.Additionally,the effect of supply voltage on charge collection is also investigated.It is concluded that the supply voltage mainly affects the bipolar gain of the parasitical bipolar junction transistor（BJT） and the existence of the source plays an important role in supply voltage variation.

Photoelectrochemical evaluation of SILAR-deposited nanoporous BiVO4 photoanodes for solar-driven water splitting

We report a photoelectrochemical investigation of BiVO4 photoanodes prepared by successive ionic layer adsorption and reaction(SILAR),a facile method that yields uniform nanoporous films.After characterization of the phase,morphology,composition,and optical properties of the prepared films,the efficiencies of charge separation(ηsep)and water oxidation(ηox)in solar water splitting cells employing these photoanodes were estimated following a previously reported procedure.Unexpected wavelength and illumination direction dependencies were discovered in the derived efficiencies,casting doubt on the validity of the analysis.An alternative approach using a diffusion–reaction model that explicitly considers the efficiency of electron collection resolved the discrepancies and explained the illumination direction dependence of the photocurrent.Electron diffusion lengths(Ln)of 0.45μm and 0.55μm were derived for pristine and cobalt phosphate(Co-Pi)modified BiVO4,respectively,which are much shorter than the film thickness of^2.1μm.The Co-Pi treatment also increasedηoxfrom 0.86 to^1,which is the main reason for the overall performance enhancement caused by adding Co-Pi.These findings suggest that there is little scope for improving the performance of SILAR-deposited BiVO4 photoanodes by further catalyzing water oxidation,but enhanced performance is achievable if electron transport can be improved.

A single-event transient induced by a pulsed laser in a silicon-germanium heterojunction bipolar transistor

A study on the single event transient （SET） induced by a pulsed laser in a silicon-germanium （SiGe） heterojunction bipolar transistor （HBT） is presented in this work. The impacts of laser energy and collector load resistance on the SET are investigated in detail. The waveform, amplitude, and width of the SET pulse as well as collected charge are used to characterize the SET response. The experimental results are discussed in detail and it is demonstrated that the laser energy and load resistance significantly affect the SET in the SiGe HBT. Furthermore, the underlying physical mechanisms are analyzed and investigated, and a near-ideal exponential model is proposed for the first time to describe the discharge of laser-induced electrons via collector resistance to collector supply when both base-collector and collector-substrate junctions are reverse biased or weakly forward biased. Besides, it is found that an additional multi-path discharge would play an important role in the SET once the base-collector and collector-substrate junctions get strongly forward biased due to a strong transient step charge by the laser pulse.