A New Proportional Base Drive Technique for SiC Bipolar Junction Transistor

A simple technique to measure the minority carrier mobility using a bipolar junction transistor is demonstrated. By fixing the base-emitter voltage, the carrier injection into the base is constant. The collector current is then monitored as a function of a magnetic field applied perpendicular to the current transport across the base. The magnetic field leads to an increase in base transit time and a corresponding decrease in collector current. From the resulting fractional change in collector current, the minority carrier mobility in the base can be determined. For narrow base transistors, quasiballistic transport across the base must be taken into account when determining the bulk minority carrier mobility.

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.

SiC bipolar junction transistors (BJTs) were fabricated based on the design criterion proposed in our previous study, which quantitatively proved the importance of decreasing a base spreading resistance. To reduce the base spreading resistance,Al <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -implantation was performed in the parasitic base region. No negative influences due to the implantation damage on the current gain were confirmed when the implantation is performed sufficiently apart from the emitter mesa sidewall, the distance of which is longer than 3 μm. Since the fabricated BJTs satisfied the design criterion, clear conductivity modulation was achieved, resulting in a reduced collector-resistance, that is, 50% of the unipolar resistance. In addition, we experimentally demonstrated that the conductivity modulation in SiC BJTs could be enhanced by decreasing the base spreading resistance.

Bipolar junction transistors (BJTs) of 4H-SiC, with a low collector-emitter forward voltage drop VCE have been fabricated without base contact implantation. A comparison of BJTs on the same wafer with and without base contact implantation shows less than 10% higher VCE for the BJTs without base contact implantation. Omitting the base contact implantation eliminates high concentrations of implantation-induced defects that act as recombination centers. This is advantageous because it allows a shorter distance Wp+ between the emitter edge and the base contact, without affecting the current gain when no base contact implantation is used. The BJTs without contact implantation show a constant current gain as Wp+ was reduced from 3 to 1 mum, whereas the gain decreased by 45% for the BJTs with base contact implantation for the same reduction of Wp+. A key to the successful fabrication of low-forward-voltage-drop SiC BJTs without base contact implantation is the formation of low-resistivity Ni/Ti/Al ohmic contacts to the base. The contact resistivity on the base region (NA ap 4 times1017 cm-3) was measured with linear transmission line method structures to rhoC = 1.9 times 10-3 Omegacm2, whereas the contact resistivity with the base contact implantation was rhoC = 1.3 times 10-4 Omegacm2, both after rapid thermal processing annealing at 800degC.

The passivation of self-aligned InGaAs/InP heterostructure bipolar transistors (HBTs) with graded base by the combination of S and low-temperature deposited SiNx was investigated. Base current was found to decrease after the passivation. Collector current significantly increases at low base-emitter voltages. The increase is attributed to the leakage current of the base-collector diode. The current gain was found to increase. When annealing was performed at 300 °C for 5 min, the base current decreases further and the collector current decreases. The leakage of collector current was found to be suppressed. The current gain was further improved and the leakage current can affect the Gummel plots. The leakage source was identified to be the interface between the semiconductor and the SiNx layer. The leakage current can be decreased by the annealing process.

Ion implantation for selective doping of SiC is problematic due to damage generation during the process and low activation of dopants. In SiC bipolar junction transistor (BJT) the junction termination extension (JTE) can be formed without ion implantation using instead a controlled etching into the epitaxial base. This etched JTE is advantageous because it eliminates ion implantation induced damage and the need for high temperature annealing. However, the dose, which is controlled by the etched base thickness and doping concentration, plays a crucial role. In order to find the optimum parameters, device simulations of different etched base thicknesses have been performed using the software Sentaurus Device. A surface passivation layer consisting of silicon dioxide, considering interface traps and fixed trapped charge, has been included in the analysis by simulations. Moreover a comparison with measured data for fabricated SiC BJTs has been performed.

The impact of bias configuration on DC operating point in large-signal operation is analyzed for Horizontal Current Bipolar Transistor (HCBT) by time-domain load-pull measurements at 2.4 GHz. The two limiting cases, constant base-emitter voltage (c-VBE) and constant base current (c-I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ), are investigated with respect to where the hard-limitation occurs, in the cut-off or saturation region. For the two cases, it is found that the linear operating range, in which the gain is flat, heavily depends on the hard-limitation type present. Additionally, operation above open-base breakdown voltage shows sharp decrease of DC collector current of 23 mA near compression point for c-I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> bias. Finally, the c-V BE bias shows around 5% higher collector efficiency in the back-off range while targeting the same output power in I-dB compression point.

Silicon carbide (SiC) semiconductor devices for high power are becoming more mature and are now commercially available as discrete devices. Schottky diodes have been on the market since a few years but also bipolar junction transistors (BJTs), JFETs and MOSFETs are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The BJTs have low conduction losses, fast switching capability, operate in normally-off mode, have high radiation hardness, and can handle high power density.This paper will review the current state of the art in active switching device performance with special emphasis on BJTs. Device performance has been demonstrated over a wide temperature interval. A very important feature in high power switch applications is the low on-resistance of a device. Better material quality and epi processes suppress the amount of basal plane dislocations to avoid stacking fault formation generated during high current injection. This has long been a concern for bipolar SiC devices but several research reports and long term reliability measurements of pn-junctions show that the bipolar degradation problem can be solved by a fine-tuned epitaxial technique. A discussion on surface passivation control is included.Finally, an example of a power switching module is given also demonstrating the excellent paralleling capability of BJTs.

Using constant base current as a boundary condition, a one-dimensional numerical simulation technique based on the conventional transport equations was developed. Transistor current-voltage curves with base current density as the variable parameter, similar to the experimental data taken from a curve tracer, are obtained. The simulation also produces transistor characteristics, especially base modulation effects, that cannot be obtained easily by using constant base voltage as a boundary condition.

Compact Modeling of Physical Mechanisms Present in the Weak Breakdown Regime of Advanced Si and SiGe Bipolar Transistors

The wide bandgap (WBG) semiconductor SiC has been identified as a potential candidate for use in high power and high frequency devices due to its superior material parameters. SiC has a breakdown field almost six times higher than that of Si or GaAs resulting in a higher attainable power density. SiC has a larger thermal conductivity, 3 times that of Si and 6 times that of GaAs, translating into a smaller chip size and, therefore, more efficient systems. To date, most research on SiC RF devices has focused on majority carrier devices such as SITs and MESFETs. There are only a few reports on SiC bipolar transistors and these studies have concentrated on SiC power switching transistors. Bipolar transistors have potentially superior linearity as well as higher current handling and power density capabilities compared to the aforementioned RF devices making BJTs ideal for use in power amplifiers.

As part of a program to develop high temperature electronics for geothermal well instrumentation, a number of solid state diode and transistor types were characterized from room temperature to 300/sup 0/C. The temperature dependence and aging stability of transport and leakage properties were measured. Included in the study were silicon diodes, bipolar transistors, JFETs, MOSFETs, and GaAs MESFETs and JFETs. In summary the results are: diodes and bipolar transistors became extremely leaky at high temperature and are therefore of limited use; silicon MOSFETs and GaAs devices showed unacceptable aging instabilities at high temperatures; silicon JFETs from certain manufacturers were sufficiently stable and had suitable temperature dependent characteristics so that operational circuits could be made. Comparisons were made of experimental device characteristics and those predicted by theory. The theoretical calculations were done using standard equations revised to include appropriate temperature dependent parameters. Close agreement between theory and experiment was found, indicating that unexpected high temperature effects were insignificant. In order to facilitate the use of devices in high temperature hybrids, it was necessary to develop bonding and prescreening techniques. A large variance of JFET 300/sup 0/C operating parameters was found even within a single production lot. Consequently, high temperature prescreening allowed each circuit to be specifically ''pretuned.'' Standard solder, epoxy, and chip and wire attachment technologies were not functional at 300/sup 0/C. Gold-germanium solder, aluminum wire to DuPont 9910 gold film, and diffusion barrier pads were developed to allow high temperature attachment.

We proposed and demonstrated a novel bistable transistor−the quantum-switched heterojunction bistable bipolar transistor. The transistor has two current states. With increasing base-emitter voltage, the collector current is switched from high to low, while the base current is switched from low to high. Bistability is observed for a certain range of base voltage. This device has potential applications in implementing high-speed single bipolar transistor memories, gain quenching in light-emitting devices, and optoelectronic switching.

A multi-differential operational amplifier, called OAmp3, designed for operation at temperatures up to minus 197 °С and developed on bipolar transistors and junction field-effect transistors of the master slice array МН2ХА030, is considered in the article. The circuitry features of the OAmp3 allow, due to the use of various negative feedback circuits, to implement a set of functions necessary for signal processing on a single amplifier: amplification (or current – voltage conversion), filtering, shift of the constant output voltage level. The performed measurements of OAmp3, connected as instrumentation amplifier circuit, showed that all manufactured products retain their performance in the temperature range from minus 150 °С to 20 °С, and individual samples – at minus 197 °С. It was found that the main reason for the loss of OAmp3 performance is an increase of the resistance of semiconductor resistors by almost 5.4 times at minus 197 °С compared to normal conditions and decrease in the junction field-effect transistor drain current. Together, these factors lead to decrease in the current consumption of the OAmp3 by almost 31 times at minus 180 °С compared to normal conditions. To reduce the temperature dependence of the current consumption and, thus, save the OAmp3 operability at low temperatures without changing the technological route of integrated circuits manufacturing, it is proposed to replace high-resistance semiconductor resistors with “pinch-resistors” formed on a small-signal p-junction field-effect transistor. The article presents the OAmp3 connection circuit in the form of an instrumental amplifier, the method and results of low-temperature measurements of experimental samples.

A bipolar junction transistor (BJT) and its operation are fundamental concepts for the understanding of power electronics (industrial electronics), transistor-transistor logic (TTL), electronic switching, and signal amplification in modern electronics. Previous research showed that non-major engineering, computer, electronic, and electrical engineering students could not understand the basic concepts involved in a BJT. This paper describes the development of a two-tier diagnostic test, the test’s administration, limitations, the participants’ detailed context, and findings from a study that explores Myanmar and Thai second-year undergraduate students’ understanding of BJT working principles and applications. The results revealed that many students in both countries had the same alternative conceptions about collector current in each operation mode of the BJT. Some alternative conceptions differ from the previous research, such as a) the collector current does not depend on the base current in cut-off mode, and b) changing the collector current does not depend on the base current in active mode, but it depends on the collector supply voltage. These research findings provide valuable information and instruments for teachers to insight, prevent, and correct the alternative conceptions proposed by students.