Junction temperature dependence of high-frequency noise inheterojunction bipolar transistors

The use of the Hawkins model, under isothermal condition, to calculate the bias dependent high frequency noise in Heterojunction Bipolar Transistors (HBTs) is questioned. The inclusion of thermal effects into the noise model of HBTs is necessary as the temperature of the device becomes progressively different from the ambient temperature with increasing bias current. Calculation of noise figure by including the thermal effects explains the experimental measurement whereas the isothermal calculation underestimates the noise figure at high bias current     

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.     

Characterization and modeling of bias-stressed InGaP/GaAs collector-up tunneling-collector HBTs fabricated with boron-ion implantation

To characterize and model the degradation of collector-up (C-up) heterojunction bipolar transistors (HBTs), we bias stress InGaP/GaAs C-up tunneling-collector HBTs (TC-HBTs) fabricated under various conditions for etching the collector mesas and of implanting boron ions into the extrinsic emitter. Contrary to the previous reports on reduction in collector current I/sub C/ of bias-stressed emitter-up HBTs fabricated with ion implantation, no I/sub C/ Gummel shift is observed in the case of C-up TC-HBTs, probably due to the lower damage resulting from the lower ion dosage. On the other hand, the base current of the bias-stressed C-up TC-HBTs increases with the decrease of the ion dose and with the increase of the collector mesa undercut under the collector electrode that is also used as an implant mask. We attribute the increased base current to the increased carrier recombination at the extrinsic base surface. Making the area of the emitter-base junction smaller than that of the base-collector junction-using electron-cyclotron resonance plasma etching together with lateral spreading of heavily implanted boron ions-results in a stable current gain even after a 1030-h testing at a junction temperature of 210/spl deg/C and a collector current density of 40/sup 2/kA/cm.     

Low-frequency noise characteristics of p-n-p InAlAs/InGaAs HBTs

The low-frequency noise characteristics of p-n-p InAlAs/InGaAs heterojunction bipolar transistors (HBTs) were investigated. Devices with various geometries were measured under different bias conditions. The base noise current spectral density (3.11 /spl times/ 10/sup -16/ A/sup 2//Hz) was found to be higher than the collector noise current spectral density (1.48 /spl times/ 10/sup -16/ A/sup 2//Hz) at 10 Hz under low bias condition (I/sub C/=1 mA, V/sub EC/=1 V), while the base noise current spectral density (2.04 /spl times/ 10/sup -15/ A/sup 2//Hz) is lower than the collector noise current spectral density (7.87 /spl times/ 10/sup -15/ A/sup 2//Hz) under high bias condition (I/sub C/=10 mA, V/sub EC/=2 V). The low-frequency noise sources were identified using the emitter-feedback technique. The results suggest that the low-frequency noise is a surface-related process. In addition, the dominant noise sources varied with bias levels.     

A comparison of low-frequency noise characteristics and noise sources in NPN and PNP InP-based heterojunction bipolar transistors

Low-frequency noise characteristics of NPN and PNP InP-based heterojunction bipolar transistors (HBTs) were investigated. NPN HBTs showed a lower base noise current level (3.85 /spl times/ 10/sup -17/ A/sup 2//Hz) than PNP HBTs (3.10 /spl times/ 10/sup -16/ A/sup 2//Hz), but higher collector noise current level (7.16 /spl times/ 10/sup -16/ A/sup 2//Hz) than PNP HBTs (1.48 /spl times/ 10/sup -16/ A/sup 2//Hz) at 10 Hz under I/sub C/=1 mA, V/sub C/=1 V. The NPN devices showed a weak dependence I/sub C//sup 0.77/ of the collector noise current, and a dependence I/sub B//sup 1.18/ of the base noise current, while the PNP devices showed dependences I/sub C//sup 1.92/ and I/sub B//sup 1.54/, respectively. The dominant noise sources and relative intrinsic noise strength were found in both NPN and PNP InP-based HBTs by comparing the noise spectral density with and without the emitter feedback resistor. Equivalent circuit models were employed and intrinsic noise sources were extracted. The high base noise current of PNP HBTs could be attributed to the exposed emitter periphery and higher electron surface recombination velocity in P-type InP materials, while the relatively high collector noise current of NPN HBTs may be due to the noise source originating from generation-recombination process in the bulk material between the emitter and the collector.     

Microwave noise characterisation of poly-emitter bipolar junction transistors

The microwave noise characteristics of poly-emitter bipolar junction transistors have been evaluated in a 0.8 mu m silicon BiCMOS process, at frequencies between 1 and 5.6 GHz and for collector currents between 0.5 and 15 mA. Using a small-signal model for the poly-emitter bipolar junction transistors, very good agreement has been obtained between measurements and calculations of both noise figure (F/sub MIN/) against frequency, and F/sub MIN/ against collector current. It is found that F/sub MIN/ was 2.3 dB at 1 GHz and 8.3 dB at 5.6 GHz for a collector current of 5 mA.<>     

InAlAs/InGaAs HBTs with simultaneously high values of F/sub /spl tau// and F/sub max/ for mixed analog/digital applications

We report the design, fabrication, and measurement of InAlAs/InGaAs heterostructure bipolar transistors (HBTs) designed for high speed digital circuits. At 0.96 V V/sub CE/ the current gain cutoff frequency, f/sub /spl tau//, is 300 GHz and the maximum frequency of oscillation, f/sub max/, is 235 GHz. This value of f/sub /spl tau//, is the highest reported for bipolar transistors. At a slightly higher V/sub CE/ bias, a high value of 295 GHz for f/sub /spl tau// and f/sub max/ were obtained simultaneously.     

Thermal dependence of HBT high-frequency performance

The effects of power dissipation and thermal resistance on device junction temperature are introduced for the first time in modelling the high-frequency performance of heterojunction bipolar transistors (HBTs). Simulated low-bias (V/sub cb/=0 V)f/sub T//J/sub c/ characteristics using the proposed model are consistent with previously reported results. This model extends previous calculations to include typical high-bias operating conditions where dramatic thermal effects are demonstrated.<>     

Relation between low-frequency noise and long-term reliability ofsingle AlGaAs/GaAs power HBTs

Self-aligned AlGaAs/GaAs single heterojunction bipolar transistors (HBTs) were fabricated using an advanced processing technology for microwave and millimeter-wave power applications. These devices were processed simultaneously, on different epilayers with similar layer structure design supplied from different vendors. They showed similar dc characteristics (current gain, β=30) and their microwave performance was also identical (f_T=60 GHz, f_max=100 GHz). The HBTs showed different noise and reliability characteristics depending on their epilayer origin. HBT's from the high-reliability wafer showed MTTF of 10⁹ h at junction temperature of 120°C. They also presented very small 1/f noise with corner frequencies in the range of a few hundred Hz. Devices were subjected to bias and temperature stress for testing their noise and reliability characteristics. Stressed and unstressed devices showed generation-recombination noise with activation energies between 120-210 meV. Stress was found to increase the generation-recombination noise intensity but not its activation energy. These HBTs did not show any surface-related noise indicating that processing did not significantly influence noise characteristics. It was found that the base noise spectral density at low frequency can be correlated to the device long term reliability     

Microwave and noise performance of SiGe BiCMOS HBT under cryogenic temperatures

In this letter, the microwave and noise performance of SiGe heterojunction bipolar transistors (HBTs) has been characterized when cooling down the temperature. It was found that SiGe HBTs (fabricated in the framework of BiCMOS process) exhibit a maximum oscillation frequency f/sub max/ of about 292 GHz at 78 K, which represents an increase of about 30% with the value measured at room temperature. The noise performance has also been characterized at cryogenic temperatures, using an original de-embedding approach. Then, using the Hawkin's noise model in conjunction with an accurate small signal equivalent extraction, the four noise parameters have been estimated. The noise figure with a 50 /spl Omega/ source impedance was measured to be equal to 1.5 dB at 40 GHz at 78 K, which is one of the lowest value reported for BiCMOS SiGe HBT in the millimeter-wave range.     

Reliability of AlInAs/GaInAs heterojunction bipolar transistors

The reliability of high-performance AlInAs/GaInAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE) is discussed. Devices with a base Be doping level of 5×10¹⁹ cm^-3 and a base thickness of approximately 50 nm displayed no sign of Be diffusion under applied bias. Excellent stability in DC current gain, device turn-on voltage, and base-emitter junction characteristics was observed. Accelerated life-test experiments were performed under an applied constant collector current density of 7×10⁴ A/cm² at ambient temperatures of 193, 208, and 328°C. Junction temperature and device thermal resistance were determined experimentally. Degradation of the base-collector junction was used as failure criterion to project a mean time to failure in excess of 10⁷ h at 125°C junction temperature with an associated activation energy of 1.92 eV     

Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173K相似文献   

Failure mode analysis of AlGaAs/GaAs HBTs using electrostatic discharge method

The failure modes of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) showing increases of base leakage current found during the bias and temperature reliability test have been examined and analysed by using an electrostatic discharge (ESD) method. In the examination for HBT having an emitter of 2 × 20 μm, increases of a base leakage current have been observed when an ESD of around 100 V is applied through a base-emitter junction. Furthermore, increases of a collector leakage current have been observed with the additional ESD of around 150 V. Since no fatal effects for the transistor amplification are found in the high current region, the degradations are concluded to be responsible to the local damages of the base layer at the edge of base-emitter junction. Applying the Wunsch-Bell model to the damaged region, the temperature is estimated to be in a range from 400 to 550°C. It is thought that thermal destruction occurs in a base layer.     

An improved SPICE model for high-frequency noise of BJTs and HBTs

An improved compact model for the high-frequency noise of bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs) is presented and implemented in SPICE3. It properly takes into account the frequency function of thermal noise in the input circuit, which is related to the real part of the input admittance. This quantity is the result of an interplay between the base resistance, the internal emitter-base capacitance, the small-signal input conductance of the intrinsic transistor, and the emitter series resistance. This requires the replacement of the noisy base resistance in SPICE by a frequency-dependent expression consisting of the appropriate SPICE parameters. A similar substitution is needed in the output circuit. For a Si/SiGe HBT these improvements lead to excellent agreement between the noise figure and device simulation results     

Thermal design studies of high-power heterojunction bipolartransistors

A theoretical thermoelectro-feedback model has been developed for the thermal design of high-power GaAlAs/GaAs heterojunction bipolar transistors (HBTs). The power-handling capability, thermal instability, junction temperature, and current distributions of HBTs with multiple emitter fingers have been numerically studied. The calculated results indicate that power HBTs on Si substrates (or with Si as the collector) have excellent potential power performance and reliability. The power-handling capability on Si is 3.5 and 2.7 times as large as that on GaAs and InP substrates, respectively. The peak junction temperature and temperature difference on the chip decrease in comparison to the commonly used Si homostructure power transistor with the same geometry and power dissipation. Thereby HBTs are promising for high-speed microwave and millimeter-wave applications. It has been also found that the nonuniform distribution of junction temperature and current can be greatly improved by a ballasting technique that uses unequal-valued emitter resistors     

A back-wafer contacted silicon-on-glass integrated bipolar process. Part II. A novel analysis of thermal breakdown

Analytical expressions for the electrothermal parameters governing thermal instability in bipolar transistors, i.e., thermal resistance R/sub TH/, critical temperature T/sub crit/ and critical current J/sub C,crit/, are established and verified by measurements on silicon-on-glass bipolar NPNs. A minimum junction temperature increase above ambient due to selfheating that can cause thermal breakdown is identified and verified to be as low as 10-20/spl deg/C. The influence of internal and external series resistances and the thermal resistance explicitly included in the expressions for T/sub crit/ and J/sub C,crit/ becomes clear. The use of the derived expressions for determining the safe operating area of a device and for extracting the thermal resistance is demonstrated.     

Graded-SiGe-base, poly-emitter heterojunction bipolar transistors

Si/Si_1-xGe_x heterojunction bipolar transistors (HBTs) fabricated using a low-temperature epitaxial technique to form the SiGe graded-bandgap base layer are discussed. These devices were fabricated on patterned substrates and subjected to annealing cycles used in advanced bipolar processing. These devices, which have base widths under 75 mm, were found to have excellent junction qualities. Due to the small bandgap of SiGe, the collector current at low bias is ten times higher than that for Si-base devices that have a pinched base resistance. This collector current ratio increases to more than 40 at LN₂ temperature resulting in current gains of 1600 for the SiGe-base transistors despite base sheet resistances as low as 7.5 kΩ/□     

An investigation of low-frequency noise in complementary SiGe HBTs

We present a comprehensive investigation of low-frequency noise behavior in complementary (n-p-n + p-n-p) SiGe heterojunction bipolar transistors (HBTs). The low-frequency noise of p-n-p devices is higher than that of n-p-n devices. Noise data from different geometry devices show that n-p-n transistors have an increased size dependence when compared with p-n-p transistors. The 1/f noise of p-n-p SiGe HBTs was found to have an exponential dependence on the (intentionally introduced) interfacial oxide (IFO) thickness at the polysilicon-to-monosilicon interface. Temperature measurements as well as ionizing radiation were used to probe the physics of 1/f noise in n-p-n and p-n-p SiGe HBTs. A weak temperature dependence (nearly a 1/T dependence) of 1/f noise is found in both n-p-n and p-n-p devices with cooling. In most cases, the magnitude of 1/f noise is proportional to I/sub B//sup 2/. The only exception in our study is for noise in the post-radiation n-p-n transistor biased at a low base current, which exhibits a near-linear dependence on I/sub B/. In addition, in proton radiation experiments, the 1/f noise of p-n-p devices was found to have higher radiation tolerance than that of n-p-n devices. A two-step tunneling model and a carrier random-walk model are both used to explain the observed behavior. The first model suggests that 1/f noise may be caused by a trapping-detrapping process occurring at traps located inside IFO, while the second one indicates that noise may be originating from the emitting-recapturing process occurring in states located at the monosilicon-IFO interface.     

Integrated circuit technology options for RFICs-present status andfuture directions

This paper will summarize the technology tradeoffs that are involved in the implementation of radio frequency integrated circuits for wireless communications. Radio transceiver circuits have a very broad range of requirements-including noise figure, linearity, gain, phase noise, and power dissipation. The advantages and disadvantages of each of the competing technologies-Si CMOS and bipolar junction transistors (BJTs), Si/SiGe HBTs and GaAs MESFETs, PHEMTS and HBTs will be examined in light of these requirements     

Improvements in direct-current characteristics of Al/sub 0.45/Ga/sub 0.55/As-GaAs digital-graded superlattice-emitter HBTs with reduced turn-on voltage by wet oxidation

Heterojunction bipolar transistors (HBTs) having an Al/sub 0.45/Ga/sub 0.55/As-GaAs digital-graded superlattice (DGSL) emitter along with an InGaP sub-emitter are reported. The band diagram of the DGSL emitter is analyzed by using a transfer matrix method and the theoretical result is consistent with the experimental observation that the DGSL emitter smoothes out the potential spike at the emitter-base junction. Such passivated HBTs with a high Al-fraction passivation layer exhibit a small offset voltage of 50 mV, a turn-on voltage of 0.87 V, and a current gain of 385. The HBTs are examined by wet-oxidizing the exposed passivated region under various conditions. Experimental results reveal that the HBTs with an exposed high Al-fraction emitter are sensitive to the ambient air. However, with InGaP capped upon the high Al-fraction emitter, the HBTs exhibit better oxidation quality. The wet oxidation brings forth the most remarkable improvements for the InGaP-capped HBTs when the passivation layer is totally wet oxidized. Furthermore, some devices from the same chip have undergone nitrogen treatment for comparison.