Bulk and surface damages in complementary bipolar junction transistors produced by high dose irradiation

Two complementary types NPN and PNP of bipolar junction transistors （BJTs） were exposed to higll dose of neutrons and gamma rays. The change in the base and collector currents, minority carriers lifetime, and current gain factor/3 with respect to the dose were analyzed. The contributions of the base current according to the defect types were also reported. It was declared that the radiation effect of neutrons was almost similar between the two transistor types, this effect at high dose may decrease the value of/3 to less than one. The Messenger-Spratt equation was used to describe the experimental results in this case. However, the experimental data demonstrated that the effect of gamma rays was generally higher on NPN than PNP transistors. This is mainly attributed to the difference in the behavior of the trapped positive charges in the SiO2 layers. Meanwhile, this difference tends to be small for high gamma dose.

Radiation effects of 50-MeV protons on PNP bipolar junction transistors

The effects of radiation on 3 CG110 PNP bipolar junction transistors(BJTs)are characterized using 50-Me V protons,40-Me V Si ions,and 1-Me V electrons.In this paper,electrical characteristics and deep level transient spectroscopy(DLTS)are utilized to analyze radiation defects induced by ionization and displacement damage.The experimental results show a degradation of the current gain and an increase in the types of radiation defect with increasing fluences of 50-Me V protons.Moreover,by comparing the types of damage caused by different radiation sources,the characteristics of the radiation defects induced by irradiation show that 50-Me V proton irradiation can produce both ionization and displacement defects in the 3 CG110 PNP BJTs,in contrast to 40-Me V Si ions,which mainly generate displacement defects,and 1-Me V electrons,which mainly produce ionization defects.This work provides direct evidence of a synergistic effect between the ionization and displacement defects caused in PNP BJTs by 50-Me V protons.

Machine learning-based analyses for total ionizing dose effects in bipolar junction transistors

Machine learning methods have proven to be powerful in various research fields.In this paper,we show that research on radiation effects could benefit from such methods and present a machine learning-based scientific discovery approach.The total ionizing dose(TID)effects usually cause gain degradation of bipolar junction transistors(BJTs),leading to functional failures of bipolar integrated circuits.Currently,many experiments of TID effects on BJTs have been conducted at different laboratories worldwide,producing a large amount of experimental data which provides a wealth of information.However,it is difficult to utilize these data effectively.In this study,we proposed a new artificial neural network(ANN)approach to analyze the experimental data of TID effects on BJTs An ANN model was built and trained using data collected from different experiments.The results indicate that the proposed ANN model has advantages in capturing nonlinear correlations and predicting the data.The trained ANN model suggests that the TID hardness of a BJT tends to increase with base current I.A possible cause for this finding was analyzed and confirmed through irradiation experiments.

Radiation-induced 1/f noise degradation of PNP bipolar junction transistors at different dose rates

It is found that ionizing-radiation can lead to the base current and the 1/f noise degradations in PNP bipolar junction transistors. In this paper, it is suggested that the surface of the space charge region of the emitter-base junction is the main source of the base surface 1/f noise. A model is developed which identifies the parameters and describes their interactive contributions to the recombination current at the surface of the space charge region. Based on the theory of carrier number fluctuation and the model of surface recombination current, a 1/f noise model is developed. This model suggests that 1/f noise degradations are the result of the accumulation of oxide-trapped charges and interface states. Combining models of ELDRS, this model can explain the reason why the 1/f noise degradation is more severe at a low dose rate than at a high dose rate. The radiations were performed in a Co60 source up to a total dose of 700 Gy（Si）. The low dose rate was 0.001 Gy（Si）/s and the high dose rate was 0.1 Gy（Si）/s. The model accords well with the experimental results.

Fabrication and characterization of 4H-SiC bipolar junction transistor with double base epilayer

In this paper we report on a novel structure of a 4H-SiC bipolar junction transistor with a double base epilayer that is continuously grown. The measured dc common-emitter current gain is 16.8 at Ic = 28.6 mA （Jc = 183.4 A/cm2）, and it increases with the collector current density increasing. The specific on-state resistance （Rsp-on） is 32.3 mΩ.cm2 and the open-base breakdown voltage reaches 410 V. The emitter N-type specific contact resistance and N＋ emitter layer sheet resistance are 1.7× 10-3 Ω.cm2 and 150 Ω/□, respectively.

Two-dimensional analysis of the interface state effect on current gain for a 4H-SiC bipolar junction transistor

This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.

Low Gate Voltage Operated Multi-emitter-dot H^+ Ion-Sensitive Gated Lateral Bipolar Junction Transistor

A low gate voltage operated multi-emitter-dot gated lateral bipolar junction transistor （BJT） ion sensor is proposed. The proposed device is composed of an arrayed gated lateral BJT, which is driven in the metal-oxidesemiconductor field-effect transistor （MOSFET）-BJT hybrid operation mode. Further, it has multiple emitter dots linked to each other in parallel to improve ionic sensitivity. Using hydrogen ionic solutions as reference solutions, we conduct experiments in which we compare the sensitivity and threshold voltage of the multi-emitter-dot gated lateral BJT with that of the single-emitter-dot gated lateral BJT. The multi-emitter-dot gated lateral BJT not only shows increased sensitivity but, more importantly, the proposed device can be operated under very low gate voltage, whereas the conventional ion-sensitive field-effect transistors cannot. This special characteristic is significant for low power devices and for function devices in which the provision of a gate voltage is difficult.

A novel 4H-SiC lateral bipolar junction transistor structure with high voltage and high current gain

In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor （LBJT） with a base tield plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3 × 1017 cm 3 are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT （VBJT） with comparable breakdown voltage （3357 V） shows that the minimum base width of 0.25 ~tm and base doping as high as 8 × 10^17 cm^-3 contribute to a maximum current gain of only 128.

Thermal analytic model of current gain for bipolar junction transistor-bipolar static induction transistor compound device

This paper proposes a thermal analytical model of current gain for bipolar junction transistor-bipolar static induction transistor （BJT-BSIT） compound device in the low current operation. It also proposes a best thermal compensating factor to the compound device that indicates the relationship between the thermal variation rate of current gain and device structure. This is important for the design of compound device to be optimized. Finally, the analytical model is found to be in good agreement with numerical simulation and experimental results. The test results demonstrate that thermal variation rate of current gain is below 10% in 25 ℃-85 ℃ and 20% in -55 ℃-25 ℃.

Model of radiation-induced gain degradation of NPN bipolar junction transistor at different dose rates

Ionizing-radiation-induced current gain degradation in NPN bipolar junction transistors is due to an increase in base current as a result of recombination at the surface of the device. A model is presented which identifies the physical mechanism responsible for current gain degradation. The increase in surface recombination velocity due to interface states results in an increase in base current. Besides, changing the surface potential along the base surface induced by the oxide-trapped charges can also lead to an increased base current. By combining the production mechanisms of oxide-trapped charges and interface states, this model can explain the fact that the current gain degradation is more severe at a low dose rate than at a high dose rate. The radiations were performed in a Co60 source up to a total dose of 70 krad（Si）. The low dose rate was 0.1 rad（Si）/s and the high dose rate was 10 rad（Si）/s. The model accords well with the experimental results.

High current gain 4H-SiC bipolar junction transistor

A novel 4H-SiC BJT of high current gain with a suppressing surface traps effect has been proposed. It is effective to improve the current gain due to the lower electrons density in the surface region by extending the emitter metal to overlap the passivation layer on the extrinsic base surface. The electrons trapped in the extrinsic base surface induce the degeneration of Si C BJTs device performance. By modulating the electron recombination rate, the novel structure can increase the current gain to 63.2% compared with conventional ones with the compatible process technology. Optimized sizes are an overlapped metal length of 4 m, as well as an oxide layer thickness of 50 nm.

A novel wide-dynamic-range logarithmic-response bipolar junction photogate transistor for CMOS imagers

In this paper, a new photodetector, bipolar junction photogate transistor (BJPG), is proposed for CMOS imagers. Due to an injection p+n junction introduced, the photo-charges drift through the p+n junction by the applied electronic field, and on the other hand, the p+n junction injects the carriers into the channel to carry the photo-charges. Therefore this device can increase the readout rate of the pixel signal charges and the photoelectron transferring efficiency. Using this new device, a new type of logarithmic pixel circuit is obtained with a wide dynamic range which makes photo-detector more suitable for imaging the naturally illuminated scenes. The simulations show that the photo current density of BJPG increases logarithmically with the incident light power due to the introduced injection p+n junction. The noise characteristics of BJPG are analyzed in detail and a new gate-induced noise is proposed. Based on the established numerical analytical model of noise, the power spectrum density curves are simulated.

A novel structure of a high current gain 4H-SiC BJT with a buried layer in the base

In this paper, a new structure of a 4H-SiC bipolar junction transistor （BJT） with a buried layer （BL） in the base is presented. The current gain shows an approximately 100% increase compared with that of the conventional structure. This is attributed to the creation of a built-in electric field for the minority carriers to transport in the base which is explained based on 2D device simulations. The optimized design of the buried layer region is also considered by numeric simulations.

Experimental and simulation studies of single-event transient in partially depleted SOI MOSFET

In this study, we investigate the single-event transient（SET） characteristics of a partially depleted silicon-on-insulator（PDSOI） metal-oxide-semiconductor（MOS） device induced by a pulsed laser.We measure and analyze the drain transient current at the wafer level. The results indicate that the body-drain junction and its vicinity are more SET sensitive than the other regions in PD-SOI devices.We use ISE 3D simulation tools to analyze the SET response when different regions of the device are hit. Then, we discuss in detail the characteristics of transient currents and the electrostatic potential distribution change in devices after irradiation. Finally, we analyze the parasitic bipolar junction transistor（p-BJT） effect by performing both a laser test and simulations.

Effects of orientation of substrate on the enhanced low-dose-rate sensitivity (ELDRS) in NPN transistors

The radiation effects and annealing characteristics of two types of domestic NPN bipolar junction transistors, fabricated with different orientations, were investigated under different dose-rate irradiation. The experimental results show that both types of the NPN transistors exhibit remarkable Enhanced Low-Dose-Rate Sensitivity （ELDRS）. After irradiation at high or low dose rate, the excess base current of NPN transistors obviously increased, and the current gain would degrade rapidly. Moreover, the decrease of collector current was also observed. The NPN transistor with （111} orientation was more sensitive to ionizing radiation than that with （100} orientation. The underlying mechanisms of various experimental phenomena are discussed in detail in this paper.

Analytical models for the base transit time of a bipolar transistor with double base epilayers

The doping profile function of a double base epilayer is constructed according to drift-diffusion theory. Then an analytical model for the base transit time τb is developed assuming a small-level injection based on the characteristics of the 4H-SiC material and the principle of the 4H-SiC BJTs. The device is numerically simulated and validated based on two-dimensional simulation models. The results show that the built-in electric field generated by the double base epilayer configuration can accelerate the carriers when transiting the base region and reduce the base transit time. From the simulation results, the base transit time reaches a minimal value when the ratio of L2/L1 is about 2.

Ultra-high current gain tunneling hot-electron transfer amplifier based on vertical van der Waals heterojunctions

Due to the backscattered parasitic current from the barriers,the current gain of the widely used amplifier is far from ideal.In this work,we demonstrate a vertical Au/Al2O3/BP/MoS2 tunneling hot-electron transfer amplifier with a hot-electron emitter-base junction and a p-n junction as the base-collector barrier.Fairly monoenergetic electrons traverse through the ultrathin Al2O3 dielectric via tunneling,which are accelerated and shifted to the collector region.The devices exhibit a high current on-off ratio of>105 and a high current density(JC)of∼1,000 A/cm2 at the same time.Notably,this work demonstrates a common-emitter current gain(β)value of 1,384 with a nanowatt power consumption at room temperature,which is a record high value among the all 2D based hot-electron transistors.Furthermore,the temperature dependent performance is investigated,and theβvalue of 1,613 is obtained at 150 K.Therefore,this work presents the potential of 2D based transistors for high-performance applications.

High temperature characterization of double base epilayer 4H-SiC BJTs

Based on the material characteristics and the operational principle of the double base epilayer BJTs,and according to the drift-diffusion and the carrier recombination theory,the common emitter current gain is calculated considering four recombination processes.Then its performance is analyzed under high temperature conditions.The results show that the emitter injection efficiency decreases due to an increase in the base ionization rate with increasing temperature.Meanwhile,the SiC/SiO2 interface states and the quality of the passivation layer will affect the surface recombination velocity,and make an obvious current gain fall-off at a high collector current.

The Complete Semiconductor Transistor and Its Incomplete Forms

This paper describes the definition of the complete transistor.For semiconductor devices,the complete transistor is always bipolar,namely,its electrical characteristics contain both electron and hole currents controlled by their spatial charge distributions.Partially complete or incomplete transistors,via coined names or/and designed physical geometries,included the 1949 Shockley p/n junction transistor（later called Bipolar Junction Transistor,BJT）,the 1952 Shockley unipolar ＇field-effect＇ transistor（FET,later called the p/n Junction Gate FET or JGFET）,as well as the field-effect transistors introduced by later investigators.Similarities between the surface-channel MOS-gate FET（MOSFET） and the volume-channel BJT are illustrated.The bipolar currents,identified by us in a recent nanometer FET with 2-MOS-gates on thin and nearly pure silicon base,led us to the recognition of the physical makeup and electrical current and charge compositions of a complete transistor and its extension to other three or more terminal signal processing devices,and also the importance of the terminal contacts.

ELDRS and dose-rate dependence of vertical NPN transistor

The enhanced low-dose-rate sensitivity （ELDRS） and dose-rate dependence of vertical NPN transistors are investigated in this article. The results show that the vertical NPN transistors exhibit more degradation at low dose rate, and that this degradation is attributed to the increase on base current. The oxide trapped positive charge near the SiO2-Si interface and interface traps at the interface can contribute to the increase on base current and the two-stage hydrogen mechanism associated with space charge effect can well explain the experimental results.