Base-emitter Voltage Research Articles

Demonstration and Characterization of Bipolar Monolithic Integrated Circuits in 4H-SiC

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A monolithic bipolar integrated circuit technology employing transistor–transistor logic (TTL) is demonstrated in 4H-SiC for the first time. Operating on a 15-V power supply, as required by the higher base–emitter voltage of SiC bipolar transistors, TTL inverters with a fan-out of ten exhibit high-level noise margin <formula formulatype="inline"><tex>$(\hbox{NM}_{H})$</tex></formula> of 1.5 V and low-level noise margin <formula formulatype="inline"><tex>$(\hbox{NM}_{L})$</tex></formula> of 3.9 V at room temperature. The transient response of the fabricated SiC TTL gates is also characterized. The circuits operate satisfactorily from room temperature to above 300 <formula formulatype="inline"><tex>$^{\circ}\hbox{C}$</tex></formula>, suggesting that SiC bipolar integrated circuits are promising candidates for high-temperature applications. </para>

Simulation of the forward voltage impact on the gain of a narrow-base transistor

Equations have been derived that describe the effect of the forward emitter-base voltage of a bipolar narrow-base transistor on the current gain. The results make it possible to use the model for calculating the processes of charge transfer.

A physical model of floating body effects in polysilicon thin film transistors

Based on a closed form of the base–emitter voltage of the parasitic bipolar transistor, a physical model of floating body effects is proposed for polysilicon thin film transistors, which takes into account the polysilicon graded pn junction and the generation rate including the Poole-Frenkel effect. Simulated results by this model are in good agreement with experimental data. It is shown that the action of a parasitic bipolar transistor should be taken into account only when the channel length is short enough due to the much smaller carrier mobility in polysilicon compared with single crystalline silicon. Whereas, the parasitic bipolar transistor gain (β) increases sharply with decreasing the channel length when the channel length is less than 5μm, which is due to the rapid increase of the base transport factor (αT).

Spin-dependent transport properties in GaMnAs-based spin hot-carrier transistors

The authors have investigated the spin-dependent transport properties of GaMnAs-based “three-terminal” semiconductor spin hot-carrier transistor (SSHCT) structures. The emitter-base bias voltage VEB dependence of the collector current IC, emitter current IE, and base current IB shows that the current transfer ratio α (=IC∕IE) and the current gain β (=IC∕IB) are 0.8–0.95 and 1–10, respectively, which means that GaMnAs-based SSHCTs have current amplification capability. In addition, the authors observed an oscillatory behavior of the tunneling magnetoresistance ratio with the increasing bias, which can be explained by the resonant tunneling effect in the GaMnAs quantum well.

Role of Annealing in Constant Period of Voltage Stress on the Burn-in Effect Suppression of InGaP/GaAs Heterojunction Bipolar Transistors

Rapid thermal annealing (RTA) is proved to be more efficient in dissociating hydrogen complexes than using a constant period of voltage stress (CPVS). Without waiting for the bond breaking of complexes by minority carrier injection, RTA favors the critical base–emitter voltage (VBE) responsible for the occurrence of burn-in (BI) from 1.75 to 1.4 V and thus assists CPVS in reducing VBE by about 25% used in BI suppression. Besides eliminating the BI, the sample first prepared by RTA and followed by CPVS has larger base and collector current densities at VBE>1.1 V and reaches 6 times those at VBE>1.3 V compared with the sample only using by CPVS.

The sensitivity mechanisms of a bipolar magnetotransistor. Part 2

Investigations of a bipolar magnetotransistor have shown that its sensitivity is determined by a concentrationre-combination mechanism, depends on the magnetic induction, and increases in weak magnetic fields. When the base-emitter voltage bias is changed, the sign of the relative current sensitivity changes, and its maximum value, when measuring a magnetic field of induction 0.3 mT, amounts to 3300 T−1.

Evidence for hot electron magnetocurrent in a double barrier tunnel junction device

Hot electron transport has been studied in three terminal Ta∕TaOx∕Co∕AlOx∕Ni81Fe19 structures fabricated by magnetron sputtering through shadow masks. With the Co base and Ta collector connected together via a small resistor, the collector current contains contributions first from hot electrons injected from the Ni81Fe19 emitter, and second from a geometrical artifact that leads to tunneling from the Fermi level in the base. Both sources of collector current lead to a room temperature magnetocurrent effect. The hot electron contribution begins to dominate as the emitter-base voltage −Veb exceeds 0.3 V.

Proton radiation effects in vertical SiGe HBTs fabricated on CMOS-compatible SOI

Proton radiation effects in vertical SiGe HBTs fabricated on CMOS-compatible silicon-on-insulator (SOI) are investigated for the first time. Proton irradiation at 63 MeV is found to introduce base leakage current at low base-emitter voltage, delay the onset of Kirk effect at high injection, and increase the frequency response of SiGe HBTs on SOI. The latter two effects are in contrast to those found in conventional bulk SiGe HBTs. Proton irradiation also generates positive fixed oxide and interface charge in the buried oxide, which alters both M-1 and BV/sub CEO/ in the SiGe HBT by modulating the electric field in the collector region.

A CMOS smart temperature sensor with a 3/spl sigma/ inaccuracy of /spl plusmn/0.1/spl deg/C from -55/spl deg/C to 125/spl deg/C

A smart temperature sensor in 0.7 /spl mu/m CMOS is accurate to within /spl plusmn/0.1/spl deg/C (3/spl sigma/) over the full military temperature range of -55/spl deg/C to 125/spl deg/C. The sensor uses substrate PNP transistors to measure temperature. Errors resulting from nonidealities in the readout circuitry are reduced to the 0.01/spl deg/C level. This is achieved by using dynamic element matching, a chopped current-gain independent PTAT bias circuit, and a low-offset second-order sigma-delta ADC that combines chopping and correlated double sampling. Spread of the base-emitter voltage characteristics of the substrate PNP transistors is compensated by trimming, based on a calibration at one temperature. A high trimming resolution is obtained by using a sigma-delta current DAC to fine-tune the bias current of the bipolar transistors.

Theory of Electrothermal Behavior of Bipolar Transistors: Part I—Single-Finger Devices

A detailed theoretical and numerical analysis of the electrothermal behavior of single-finger bipolar transistors is proposed. Two models of different complexities are introduced to investigate self-heating effects in bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs) biased with a constant base-emitter voltage source or with a constant base current source. In the constant base-emitter voltage case, simple relations are derived for determining the onset of the flyback behavior in the output characteristics which defines the boundary of the safe operating region. The model indicates that the flyback behavior disappears at high V/sub BE/ values, and predicts a thermal hysteresis phenomenon at high currents. It is also shown that at high current levels the electrothermal behavior is dominated by ohmic base pushout. If a constant base current is applied, the model shows that both BJTs and HBTs are unconditionally thermally stable. The transient behavior is also considered, and the temperature evolution is investigated for different bias conditions. The model shows that, if the device is biased in the thermally unstable region, thermal breakdown occurs within a finite time instant in the limit case of a zero ballast resistance. Finally, the reduction in the safe operating area due to avalanche effects and to the temperature dependence of thermal conductivity is discussed, and a simplified model is proposed.

Theory of Electrothermal Behavior of Bipolar Transistors: Part II—Two-Finger Devices

A thorough theoretical and numerical analysis of the electrothermal behavior of two-finger bipolar transistors is presented. It is shown that thermal feedback and coupling effects introduce an additional singularity in the output I-V characteristics, namely a current bifurcation, which manifests itself as multiple solution branches emanating from a branching point. As a result, when the bifurcation condition is reached, the device is triggered in an asymmetrical operation mode in which one device carries most of the current. A unified formulation for the electrothermal behavior of a two-finger device is derived for different bias conditions at the input port: constant voltage, constant base current and constant emitter current. The analysis proofs that the critical condition defining the onset of current bifurcation is the same for all kinds of bias conditions. While operation under a constant base-emitter voltage is limited by the flyback condition, the current bifurcation condition defines the boundary of the normal operation region for the constant base current and constant emitter current cases. Finally, a rigorous method for identifying the conditions of thermal instability for an arbitrary number of emitter fingers is outlined. As an example, the method is used to derive the thermal instability conditions for the general case of temperature dependent thermal conductivity in a two-finger device.

Simultaneous Extraction of the Base and Thermal Resistances of Bipolar Transistors

A method for the simultaneous extraction of the base resistance R/sub b/ and thermal resistance R/sub th/ of bipolar transistors is described. The technique can be applied to single devices without the requirement of special structures. The measurements are based on the collector-base voltage dependence of the base-emitter voltage under constant emitter current steering and accounts for the influence of Early effect and self-heating. Results are obtained for advanced HBTs with several emitter widths enabling the extraction of R/sub th/ and the intrinsic and extrinsic contribution of R/sub b/. A detailed comparison is made with other extraction techniques and reveals an excellent agreement.

Origin of large magnetocurrent in three-terminal double-barrier magnetic tunnel junctions

Double-barrier magnetic tunnel junctions (DBMTJs) of composition Co∕AlOx∕Co∕AlOx∕Ni81Fe19 have been fabricated by magnetron sputtering through shadow masks. Two terminal measurements made upon the individual tunnel barriers revealed nonlinear I–V curves and significant room-temperature tunnel magnetoresistance (TMR) in all cases. Measurements were also performed with connections made to all three electrodes. The TMR of a particular tunnel barrier within the DBMTJ can be strongly modified by applying a bias voltage to the other barrier, while the TMR measured across the two barriers in series decreases more slowly with increasing bias voltage than for a single barrier. With zero bias applied between the central Co base electrode and the Co collector electrode, the collector current was measured as electrons were injected from the Ni81Fe19 electrode. For structures grown on Si∕SiO2 substrates, the collector current showed a nonmonotonic dependence upon the emitter-base bias voltage, and collector magnetocurrent values in excess of 100% were observed at nonzero emitter-base bias values. For structures grown on quartz the collector current increased while the magnetocurrent decreased with increasing emitter-base voltage. We suggest that the enhanced TMR and magnetocurrent effects can be explained by substrate leakage and geometrical artifacts rather than by transport of spin-polarized hot electrons across the base layer.

비정질 n형 Si 박막을 이용한 자기터널링 트랜지스터 제작과 특성

Magnetic tunneling transistor (MTT) device using the amorphous n-type Si semiconductor film for base and collector consisting of the [CoFe/NiFe](free layer) and Si(top layer) multilayers was used to study the spin-dependent hot electron magnetocurrent (MC) and tunneling magnetoresistance (TMR) at room temperature. A large MC of 40.2 % was observed at the emitter-base bias voltage ( ) of 0.62 V. The increasing emitter hot current and transfer ratio ( / ) as are mainly due to a rapid increase of the number of conduction band states in the Si collector. However, above the of 0.62 V, the rapid decrease of MC was observed in amorphous Si-based MTT because of hot electron spin-dependent elastic scattering across CoFe/Si interfaces.

A CMOS smart temperature sensor with a 3/spl sigma/ inaccuracy of /spl plusmn/0.5/spl deg/C from -50/spl deg/C to 120/spl deg/C

A low-cost temperature sensor with on-chip sigma-delta ADC and digital bus interface was realized in a 0.5 /spl mu/m CMOS process. Substrate PNP transistors are used for temperature sensing and for generating the ADC's reference voltage. To obtain a high initial accuracy in the readout circuitry, chopper amplifiers and dynamic element matching are used. High linearity is obtained by using second-order curvature correction. With these measures, the sensor's temperature error is dominated by spread on the base-emitter voltage of the PNP transistors. This is trimmed after packaging by comparing the sensor's output with the die temperature measured using an extra on-chip calibration transistor. Compared to traditional calibration techniques, this procedure is much faster and therefore reduces production costs. The sensor is accurate to within /spl plusmn/0.5/spl deg/C (3/spl sigma/) from -50/spl deg/C to 120/spl deg/C.

Impact of Collector-Base Junction Traps on Low-Frequency Noise in High Breakdown Voltage SiGe HBTs

This work investigates the impact of collector-base (CB) junction traps on low-frequency noise in high breakdown voltage (HBV) SiGe HBTs. By comparing the base current and 1/f noise at the same internal emitter-base (EB) voltage of the standard breakdown voltage (SBV) and HBV devices, we show that the CB junction traps not only increase base current, but also contribute base current 1/f noise when high injection occurs. The individual 1/f noise contributions from the emitter-base junction traps and from the collector-base junction traps are separated. The dependence of the 1/f noise component on the corresponding base current component is determined, and shown to be different for the EB and CB junction traps. The dependence of the total 1/f noise on the total base current, however, remains the same before and after high injection occurs in the HBV device, which is approximately the same as that for the SBV device. The I/sub B/ contribution from the CB junction recombination current needs to be modeled for accurate I-V and 1/f noise modeling.

Precision Temperature Measurement Using CMOS Substrate PNP Transistors

This paper analyzes the nonidealities of temperature sensors based on substrate pnp transistors and shows how their influence can be minimized. It focuses on temperature measurement using the difference between the base-emitter voltages of a transistor operated at two current densities. This difference is proportional to absolute temperature (PTAT). The effects of series resistance, current-gain variation, high-level injection, and the Early effect on the accuracy of this PTAT voltage are discussed. The results of measurements made on substrate pnp transistors in a standard 0.5-/spl mu/m CMOS process are presented to illustrate the effects of these nonidealities. It is shown that the modeling of the PTAT voltage can be improved by taking the temperature dependency of the effective emission coefficient into account using the reverse Early effect. With this refinement, the temperature can be extracted from the measurement data with an absolute accuracy of /spl plusmn/0.1/spl deg/C in the range of -50 to 130/spl deg/C.

Fabrication and characteristics of magnetic tunnel transistors using amorphous n‐type Si films

AbstractA magnetic tunnel transistor (MTT) device using an amorphous n‐type Si semiconductor film for the base and collector consisting of [CoFe/NiFe] (free layer) and Si (top layer) multilayers is used to study the spin‐dependent hot electron magnetocurrent (MC) and the tunneling magnetoresistance at room temperature. A large MC of more than 40.2% is observed at the emitter–base bias voltage VBE of 0.62 V. The increasing emitter hot current and transfer ratio with the increase of the emitter–base voltage are due mainly to a rapid creation of a number of conduction‐band states in the Si collector. However, above a VBE of 0.62 V, a rapid decrease of the MC is observed in an amorphous Si‐based MTT. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A New InP–InGaAs HBT With a Superlattice-Collector Structure

The dc characteristics of an interesting InP-InGaAs heterojunction bipolar transistor (HBT) with a superlattice (SL) structure incorporated in the base-collector (B-C) junction are demonstrated. In the SL structure, holes injected from the collector collide with holes confined in the SL and impact them out of the SL across the valence-band discontinuities. With a collector-emitter (C-E) voltage V/sub CE/ less than the C-E breakdown voltage BV/sub CE0/, the current gain can be increased at base-current inputs because the released holes from the SL inject into the base to cause the emitter-base junction operating under more forward-biased condition. An ac current gain up to 204 is obtained. At base-emitter voltage V/sub BE/ inputs, the released holes travel to the base terminal to decrease the base current. The studied HBT exhibits common-emitter current gains exceeding 47 at low current levels and useful gains spreading over seven orders of magnitude of collector current.

Sulfur and low-temperature SiNx passivation of self-aligned graded-base InGaAs/InP heterostructure bipolar transistors

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.