PNP Bipolar Transistors Research Articles

Mechanism of Degradation Rate on the Irradiated Double-Polysilicon Self-Aligned Bipolar Transistor

The latent enhanced low dose rate sensitivity (ELDRS) effect is observed in the double-polysilicon self-aligned (DPSA) technology PNP bipolar junction transistor (BJT) irradiated with a high and low dose rate gamma ray, which is discussed from the perspective of the three-stage degradation rate of the excess base current. The great degradation rate as a result of the high dose irradiation of the first stage is dominantly ascribed to the positive oxide trap charges accumulated during a short irradiation, and then due to the competition between the recombination of electrons and capture of the hole by the traps. It declined sharply into a degradation rate saturated region of the second stage. However, for the low dose rate, the small increase in the degradation rate in the first stage is caused by the holes escaping from the initial recombination and being transported to the interface to form the interface states. Then, the competition between the steadily increasing interfacial trap charge and the continuously annealed shallow level oxide trap charge leads to the stable increase of degradation under low dose irradiation. Finally, in stage three, the increases of the degradation rates for high and low dose irradiation result from the different amounts of the hydrogen molecules generated by the hole reactive with depassiviated Si suspended bonds, which can interact with the deep level defects and release protons, causing an increase of interfacial trap charges with prolonged irradiation.

A 68-nW novel CMOS sub-bandgap voltage reference circuit

This paper proposes a CMOS sub-bandgap reference (sub-BGR) circuit without resistors for ultra-low power applications. The BGR core circuit consists of a vertical PNP bipolar transistor, a temperature-compensation amplifier and a Proportional to Absolute Temperature (PTAT) voltage generator. The PTAT voltage generator consists of four p-type transistors and generates a positive temperature dependent voltage, which compensates for the negative temperature dependent base-emitter voltage in a PNP bipolar transistor. The circuit generates a sub-bandgap voltage of silicon. The sub-BGR is fabricated with 65-nm standard CMOS process with an area of 400 μm × 80 μm. Experimental results demonstrate that this sub-BGR circuit can generate a 202.8 mV reference voltage with a power consumption of 68 nW.

Mechanism of Synergistic Effects of Neutron- and Gamma-Ray-Radiated PNP Bipolar Transistors

The synergistic effects of neutron and gamma ray radiated PNP transistors are systematically investigated as functions of the neutron fluence, gamma ray dose, and dose rate. We find that the damages show a `tick'-like dependence on the gamma ray dose after the samples are radiated by neutrons. Two negative synergistic effects are derived, both of which have similar magnitudes as the ionization damage (ID) itself. The first one depends linearly on the gamma ray dose, whose slope depends quadratically on the initial displacement damage (DD) and can be attributed to the healing of neutron-radiation-induced defects in silicon. The second one has an exponential decay with the gamma ray dose, whose amplitude shows a rather strong enhanced low-dose-rate sensitivity (ELDRS) effect and can be attributed to the passivation of neutron-induced defects near the silica/silicon interface by the gamma-ray-generated protons in silica, which can penetrate the silica/silicon interface to passivate the neutron-induced defects in silicon. The simulated results based on the proposed model match the experimental data very well, but differ from previous model, which does not assume annihilation or passivation of the displacement defects. The unraveled defect annealing mechanism is important because it implies that displacement damages can be repaired by gamma ray radiation or proton diffusion, which can have important device applications in the space or other extreme environments.

A comparative study on electrical characteristics of 1-kV pnp and npn SiC bipolar junction transistors

We investigate the electrical characteristics of 1-kV pnp SiC bipolar junction transistors (BJTs) and compare them with those of npn SiC BJTs. The base resistance, current gain, and blocking capability are characterized. It is found that the base resistance of pnp SiC BJTs is two orders of magnitude lower than that of npn SiC BJTs. However, the obtained current gains are low below unity in pnp SiC BJTs, whereas npn SiC BJTs exhibit a current gain of 14 without surface passivation. The reason for the poor current gain of pnp SiC BJTs is discussed.

Discharge Characteristics of a Triple-Well Diode-String ESD Clamp

In this work, DC and transient characteristics of a 4 diode string utilizing triple-well technologies as a VDD-VSS clamp device for ESD protection are analyzed in detail based on 2-dimensional device and mixed-mode simulations. It is shown that there exists parasitic pnp bipolar transistor action in this device leading to a sudden increase in DC substrate leakage if anode bias is getting high. Through transient simulations for a 2000 V PS-mode HBM ESD discharge event, it is shown that the dominant discharge path is the one formed by a parasitic pnpn thyristor and a parasitic npn bipolar transistor in series. Percentage ratios of the various current components regarding the anode current at its current peaking are provided. The mechanisms involved in ESD discharge inside the diode-string clamp utilizing triple-well technologies are explained in detail, which has never been done anywhere in the literature based on simulations or measurements.

Impact of nitride passivation layer on ionizing irradiation damage on LPNP bipolar transistors

Bipolar junction transistors (BJTs) are generally employed in spacecraft, due to their current drive capability, linearity and excellent matching characteristics. High-energy particles and cosmic rays in space environment remarkably affect electronic devices, especially in BJTs producing total ionizing dose, displacement damage or single event effect. Among them, ionizing irradiation effects on BJTs dominates. For BJTs, ionization damage can induce the oxide trapped charges in SiO2 layer and interface traps in Si/SiO2, resulting in more recombination base current and the degradation of current gain. Consequently, the accumulation of both oxide charges and interface traps causes an increase in the base current.#br#Passivation layer is also an important factor of the irradiation effects of BJTs. Previous works only studied the degradation of electrical properties of the devices with/without passivation layer induced by irradiation, and did not give an influence mechanisms of passivation layer on the irradiation respond of devices. Therefore, the irradiation damage mechanisms of the BJTs with or without nitride passivation layer are not clear so far.#br#In this paper, the impact of Si3N4 passivation layer on ionizing irradiation damage on lateral PNP bipolar transistors (LPNP) was studied by using 60Co gamma irradiation source. The KEITHLEY 4200-SCS semiconductor parameter analyzer was used to measure the relationship between the electrical properties of LPNP transistors and ionization dose, including the Gummel characteristics, the degradation of current gain, etc. The irradiation defects of the LPNP transistors with/without passivation layer structure were analyzed by the deep level transient spectroscopy (DLTS). The experimental results show that the electrical properties of the LPNP transistors with and without passivation layer exhibit similar characteristics. For all samples, the base current increases with increasing the total dose, while the collector current does not almost change. Compared with the LPNP transistors without Si3N4 passivation layer, the degradation of LPNP transistor with Si3N4 passivation layer is severe.#br#Based on the excess base current as a function of base-emitter voltage for the LPNP transistors with/without nitride passivation layer, the degradation of bipolar transistors with nitride passivation layer is severe under the same irradiation conditions. The DLTS analyses show that compared with the bipolar transistors without nitride passivation layer, the signal peak located at about 300 K is shifted to low temperature for the bipolar transistors with nitride passivation layer. The above results show that the LPNP transistors with nitride passivation could produce a large number of interface states with the energy level is closer to the middle of the forbidden band during the irradiation, which is attributed to a large number of hydrogen presence during the processing of fabricated passivation layer.

A Comparative Study of InGaP/GaAs Collector-Up HBTs for High-Reliability Small-Scale PA Applications

In this paper, the characteristics of InGaP/GaAs collector-up (C-up) pnp and npn heterojunction bipolar transistors (HBTs) with the graded InGaAs base and the nonuniform doped collector are demonstrated, and the performances as well as the reliability of the novel HBTs have been compared with the conventional InGaP/GaAs HBTs with various collector structures and thermal schemes. Compared to conventional HBTs, the studied C-up HBTs exhibited better current-driving capability, higher RF efficiency, and improved long-term reliability. Note that the pnp device displayed greater thermal stability enhancements, which are distinct and reproducible, than the npn device. The favorable data of the pnp C-up HBT could be attributed to higher electron mobility, resulting in low base resistance and higher emitter resistance improving the thermal stability. The comparison results, based on pragmatic observations from the C-up HBTs without relatively large heat-dissipation configurations, should be very useful for the reliable and the cost-effective design as small-scale power amplifiers in the wideband CDMA system.

Analysis of deep level defects in bipolar junction transistors irradiated by 2 MeV electrons

In this work we investigate the deep level defects and the electrical characteristics of commercial PNP bipolar junction transistor (BJT) irradiated by 2MeV electrons with various fluences. The activation energy and the capture cross-section characteristics of the defects were obtained by deep level transient spectroscopy (DLTS). Five types of traps (including minority carrier traps and majority carrier traps) were observed before and after irradiation. By applying different reverse bias to the sample, the defects in the bulk and at the interface could be distinguished. The formation of such defects resulted in the degradation of the transistors-gain. Therefore the use of annealing methods at appropriate temperature was considered to recover the optimum electrical characteristics of the device.

A novel vertical SCR for ESD protection in 40 V HV bipolar process

A vertical Silicon Controlled Rectifier (VSCR) realized in a high-voltage (HV) 40V bipolar process is proposed for electrostatic discharge (ESD) protection applications. In addition, a new method is proposed to alter the layout of the emitter regions of the parasitic vertical PNP (VPNP) bipolar transistor in the VSCR to optimize the trigger voltage and the area of the VSCR. The transmission line pulsing (TLP) measurement results show that the VSCR possesses enhanced ESD robustness compared to the conventional vertical PNP (VPNP) bipolar transistor. The new VSCR can adjust trigger voltage, holding voltage and failure current with changing the number of emitter regions. Compare to VPNP bipolar transistor, the VSCR is more suitable for 40V bipolar process.

Dependence on Base Width and Doping Concentration of Current Degradation in Gate-controlled Lateral PNP Bipolar Transistors Exposed to Reactor Neutrons and Gamma Rays

Bipolar devices are widely used in the nuclear reactor control system, and the radiation effects on them are very important to reactor operation. The lateral PNP bipolar transistor is a radiation-sensitive structure in bipolar integrated devices. Its degradation under irradiation is the primary cause for functional failures of bipolar integrated devices. It is useful to understand the radiation response of the transistors to find better design strategies for radiation hardness. Three kinds of gate-controlled lateral PNP bipolar transistors (GCLPNPs) with different base widths and doping concentrations are specially designed to explore base current degradation induced by reactor neutrons and gamma rays. Dependence on base width and doping concentration of the degradation is analyzed in this work and the results are beneficial to radiation-hardening design of the lateral PNP bipolar transistor.

Impact of Passivation Layers on Irradiation Response of PNP Transistors Under Different Dose Rates

In this paper, the effect of nitride passivation layer on the irradiation response of PNP bipolar junction transistors (BJTs) by Co-60 gamma ray under high and low dose rates is investigated. In order to analyze the damage mechanisms on BJTs with or without nitride passivation layer induced by gamma rays, the excess base current and deep level transient spectroscopy are measured. Experimental results show that there is an enhanced low dose rate sensitivity for PNP transistors with and without nitride passivation layers. In addition, the degradation of PNP BJTs with nitride layer is more serious than that of PNP BJTs without nitride layer under the same irradiation condition. Compared with the PNP BJTS without nitride passivation layer, ionization effect in the PNP BJTs with nitride passivation layer can generate greater density of interface traps with deeper energy level at a given dose rate. Moreover, the irradiated BJTs under the low dose rate produces deeper energy level of interface traps than that under the high dose rate. Based on the analysis, hydrogen is an important factor influencing the dose rate sensitivity and the degradation of the BJT with nitride passivation layers.

Dependence of Ideality Factor in Lateral PNP Transistors on Surface Carrier Concentration

The influence of surface carrier concentration on the ideality factor of excess base current ( $\Delta I_{B}$ ) in gated lateral PNP (GLPNP) bipolar junction transistors (BJTs) induced by 1-MeV electrons is investigated. $\Delta I_{B}$ in LPNP BJTs is impacted by the surface carrier density and radiation-induced interface traps. In GLPNP BJTs, the surface carrier concentration can be controlled by the voltage applied to a gate over the base region. The ideality factor changes after irradiation, and its dependence on emitter-base voltage ( $V_{\mathrm {EB}}$ ) is a function of gate voltage. For the irradiated devices, as the gate voltage decreases from +20 to −5 V, the ideality factor for excess base current changes from a single slope to two-slope behavior. The majority carrier concentration at the surface of the base, controlled by the gate voltage, impacts the excess base current and its ideality factor.

Ionizing/displacement synergistic effects induced by gamma and neutron irradiation in gate-controlled lateral PNP bipolar transistors

A kind of gate-controlled lateral PNP bipolar transistor has been specially designed to do experimental validations and studies on the ionizing/displacement synergistic effects in the lateral PNP bipolar transistor. The individual and mixed irradiation experiments of gamma rays and neutrons are accomplished on the transistors. The common emitter current gain, gate sweep characteristics and sub-threshold sweep characteristics are measured after each exposure. The results indicate that under the sequential irradiation of gamma rays and neutrons, the response of the gate-controlled lateral PNP bipolar transistor does exhibit ionizing/displacement synergistic effects and base current degradation is more severe than the simple artificial sum of those under the individual gamma and neutron irradiation. Enough attention should be paid to this phenomenon in radiation damage evaluation.

The effects of gamma irradiation on neutron displacement sensitivity of lateral PNP bipolar transistors

The effects of gamma irradiation on neutron displacement sensitivity of four types of lateral PNP bipolar transistors (LPNPs) with different neutral base widths, emitter widths and the doping concentrations of the epitaxial base region are studied. The physical mechanisms of the effects are explored by defect analysis using deep level transient spectroscopy (DLTS) techniques and numerical simulations of recombination process in the base region of the lateral PNP bipolar transistors, and are verified by the experiments on gate-controlled lateral PNP bipolar transistors (GCLPNPs) manufactured in the identical commercial bipolar process with different gate bias voltage. The results indicate that gamma irradiation increases neutron displacement damage sensitivity of lateral PNP bipolar transistors and the mechanism of this phenomenon is that positive charge induced by gamma irradiation enhances the recombination process in the defects induced by neutrons in the base region, leading to larger recombination component of base current and greater gain degradation.

Radiation-induced 1/f noise degradation of PNP bipolar junction transistors at different dose rates**Project supported by the National Natural Science Foundation of China (Grant Nos. 61076101 and 61204092).

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.

On a Parasitic Bipolar Transistor Action in a Diode ESD Protection Device

In this work, we show that an excessive lattice heating problem can occur in the diode electrostatic discharge (ESD) protection device connected to a VDD bus in the popular diode input protection scheme, which is favorably used in CMOS RF ICs. To figure out the reason for the excessive lattice heating, we construct an equivalent circuit for input human-body model (HBM) test environment of a CMOS chip equipped with the diode protection circuit, and execute mixed-mode transient simulations utilizing a 2-D device simulator. We analyze the simulation results in detail to show out that a parasitic pnp bipolar transistor action relating nearby p+-substrate contacts is responsible for the excessive lattice heating in the diode protection device, which has never been focused before anywhere.

Radiation Defects and Annealing Study on PNP Bipolar Junction Transistors Irradiated by 3-MeV Protons

A combined radiation effect is produced by 3-MeV protons, giving by both ionization and displacement damage, on semiconductor devices. In this paper, electrical characteristics and deep level transient spectroscopy (DLTS) are used to measure the radiation defects induced by ionization and displacement damage during the annealing process. A nonlinear relationship between the proton fluence and radiation response is clearly observed in the 3CG110 PNP bipolar junction transistor (BJT). DLTS analysis technique and annealing response of BJTs can provide important information on the nature of the ionization and displacement-induced defects, and measure them quantitatively, especially for the BJT with the combined radiation damage induced by protons. Based on the results of DLTS measurement and current gain annealing, the evolution of the ionization and displacement defects during the irradiation and annealing process is revealed, and the relationship between defects and current gain annealing is studied.

Proton Irradiation as a Screen for Displacement-Damage Sensitivity in Bipolar Junction Transistors

NPN and PNP bipolar junction transistors of varying sizes are irradiated with 4-MeV protons and 10-keV X-rays to determine the amount of ionization-related degradation caused by protons and calculate an improved estimate of displacement-related degradation due to protons. While different ratios of degradation produced by displacement damage and ionization effects will occur for different device technologies, this general approach, with suitable margin, can be used as a screen for sensitivity to neutron-induced displacement damage. Further calculations are performed to estimate the amount of degradation produced by 1-MeV equivalent neutron displacement damage compared to that produced by the displacement damage due to protons. The results are compared to previous work.

A 0.7 V Relative Temperature Sensor With a Non-Calibrated <formula formulatype="inline"><tex Notation="TeX">$\pm 1~^{\circ}{\rm C}$</tex></formula> 3<formula formulatype="inline"><tex Notation="TeX">$\sigma$</tex></formula> Relative Inaccuracy

This paper presents a new low-voltage relative temperature sensor for multi-core digital processor on-chip thermal management in a 180 nm CMOS process. Three types of sensing diodes including Schottky barrier diode (SBD), subthreshold MOSFET diode and dynamic threshold MOSFET (DTMOS) diode have been investigated for low-voltage operation, while traditional parasitic PNP-bipolar junction transistor (BJT) diodes are implemented to provide a performance reference. A matrix of 7 $\times$ 7 small remote sensor nodes is implemented on the chip with a deployment density of 49/0.81 ${\rm mm}^{2}$ and sharing the same bias current generator, control logic, and data converter. The measured minimum supply voltage (not including the clock control block) of the sensor is 0.7 V over $-55~^{\circ}{\rm C}$ to 125 $~^{\circ}{\rm C}$ . The relative sensing inaccuracies $(3\sigma)$ without calibration are less than $\pm 1.5~^{\circ}{\rm C}$ , $\pm 1.2~^{\circ}{\rm C}$ and $\pm 1~^{\circ}{\rm C}$ for the designs based on SBD, subthreshold MOSFET, and DTMOS, respectively. To the best of the authors’ knowledge, this is the first time that non-calibrated relative sensing accuracy is reported for SBD-based and DTMOS-based temperature sensors, and the best reported result for the design based on subthreshold MOSFET. The absolute inaccuracies with calibration-per-chip are also presented. Furthermore, the multi-location thermal monitoring function has been experimentally demonstrated and a 1.8 $^{\circ}{\rm C/mm}$ on-chip temperature gradient was detected.

Radiation induced deep level defects in bipolar junction transistors under various bias conditions

Bipolar junction transistor (BJT) is sensitive to ionization and displacement radiation effects in space. In this paper, 35MeV Si ions were used as irradiation source to research the radiation damage on NPN and PNP bipolar transistors. The changing of electrical parameters of transistors was in situ measured with increasing irradiation fluence of 35MeV Si ions. Using deep level transient spectroscopy (DLTS), defects in the bipolar junction transistors under various bias conditions are measured after irradiation. Based on the in situ electrical measurement and DLTS spectra, it is clearly that the bias conditions can affect the concentration of deep level defects, and the radiation damage induced by heavy ions.