Effect of interfacial oxide thickness on 1/f noise in polysilicon emitter BJTs

The role of the interfacial oxide (IFO) between the polysilicon and monosilicon emitter regions on the noise behavior of n-p-n poly-emitter bipolar transistors was investigated through 1/f noise measurements. Bipolar junction transistors with different IFO thickness, and emitter geometry were utilized. Measurements with variable external base bias resistance (R/sub S/) were used to investigate the relative contribution of each individual noise source from the base current (S/sub IB/), the collector current (S/sub IC/) and, the internal emitter and base series resistances (S/sub Vr/). When the voltage noise power spectral densities S/sub VC/ and S/sub VB/ were measured across resistances in series with the collector and base, respectively, using a relatively large R/sub S/ (/spl sim/1 M/spl Omega/), S/sub IB/ was found to have the dominant noise contribution at lower bias currents. On the other hand, when the voltage noise power spectral densities S/sub VC/ and S/sub VE/ were measured across resistances in series with the collector and emitter, respectively, in a different experimental setup with a low R/sub S/ value, S/sub Vr/ was found to have the dominant noise contribution at higher bias currents. IFO was found to increase S/sub IB/, S/sub IC/, and S/sub Vr/. S/sub IB/ was modeled as a combination of tunneling and diffusion fluctuations of the minority carriers in the emitter; whereas S/sub IC/ was modeled as a combination of number and diffusion fluctuations of the minority carriers in the base. S/sub Vr/ was attributed to the internal emitter resistance noise originating from the fluctuation in the majority carrier flow through the IFO.     

The influence of BF2 and F implants on the 1/f noise inSiGe HBTs with a self-aligned link base

A study is made of 1/f noise in SiGe heterojunction bipolar transistors (HBTs) fabricated using selective growth (SEG) of the Si collector and nonselective growth (NSEG) of the SiGe base and Si emitter cap. The transistors incorporate a self-aligned link base formed by BF ₂ implantation into the field oxide below the p⁺ polysilicon extrinsic base. The influence of this BF₂ implant on the 1/f noise is compared with that of a F implant into the polysilicon emitter. Increased base current noise S_IB and base current are seen in transistors annealed at 975°C, compared with transistors annealed at 950 or 900°C. At a constant collector current, both the BF₂ and F implants reduce S_IB, whereas at a constant base current, only the BF₂ implant reduces S_IB. This result indicates that the BF₂ implant decreases the intensity of the base current noise source whereas the F implant decreases the base current. The proposed explanation for the increased 1/f noise is degradation of the surface oxide by viscous flow at 975°C under the influence of stress introduced during selective Si epitaxy. The influence of the BF₂ implant on the noise is explained by the relief of the stress and hence the prevention of viscous oxide flow     

1/f noise characterization of base current and emitter interfacialoxide breakup in n-p-n polyemitter bipolar transistors

We propose using base 1/f noise to characterize the distribution of diffusion and tunneling components of base-current (I_b) at the emitter poly/monosilicon interface in n-p-n polyemitter transistors. A noise model is constructed to interpret the I_b 1/f noise (S _iEB) dependence on these combined currents. Measured I_b dependences of S_iEB increase progressively from I_b^1.2 to I_b^2.0 for transistors having emitter structures concomitant with increasing current gains and series emitter resistances ranging between 115-1800 and 7-33Ω, respectively. This is indicative of tunneling components in I_b^2.0 that increase with higher interfacial oxide continuity, and persist in epitaxially realigned emitters     

Low-frequency noise in polysilicon emitter bipolar transistors

The low-frequency noise in polysilicon emitter bipolar transistors is investigated. Transistors with various geometries and various properties of the oxide layer at the monosilicon polysilicon interface are studied. The main 1/f noise source proved to be located in the oxide layer. This source causes both 1/f noise in the base current S_Ib and 1/f noise in the emitter series resistance S_re The magnitude of the 1/f noise source depends on the properties of the oxide layer. The 1/f noise is ascribed to barrier height fluctuations of the oxide layer resulting in transparency fluctuations for both minority and majority carriers in the emitter, giving rise to S_Ib and S _re respectively. It is also shown that a low transparency of the oxide layer also reduces the contribution of mobility fluctuations to S_Ib     

Measurement and comparison of 1/f noise and g-r noise in siliconhomojunction and III-V heterojunction bipolar transistors

This paper experimentally determines and compares the 1/f noise and the g-r noise, as components of the base noise current spectral density, in Si homojunction and III-V heterojunction bipolar transistors (HBTs) in common-emitter configuration. The noise spectra for each of these devices are obtained as functions of the base bias current (I_B), and the 1/f noise has been found to depend on I_B as I_B^γ, where γ~1.8 for the silicon BJT's and InP/InGaAs HBT's with high current gains (β~50), and γ~1.1 for the AlGaAs/GaAs HBTs with low current gains (4<β<12). The nearly constant current gain and the near square-law and inverse-square emitter area dependence of 1/f noise in silicon devices are indicative of the dominant base bulk recombination nature of this noise. The 1/f noise in the InP based HBTs has been found to be lowest among all the devices we have tested, and its origin is suggested to be the base bulk recombination as in the Si devices. For the AlGaAs/GaAs HBTs, the low current gain and the near unity value of γ, arise most likely due to the combined effects of surface, bulk, and depletion region recombinations and the base-to-emitter injection. The dependence of the 1/f noise on the base current density in the devices tested in this work, and those tested by others are compared to find out which HBT's have achieved the lowest level of 1/f noise     

Low-frequency noise of InP/InGaAs heterojunction bipolartransistors

The equivalent base noise SI_b of InP/InGaAs heterojunction bipolar transistors (HBT's) with a circular pattern emitter is investigated experimentally at a low frequency ranging from 10-10⁵ Hz. The measured SI_b exhibits the 1/f dependence in an overall frequency range without any accompanying burst noise. Furthermore, SI_b varies as I_b^γ for the base current I_b and as d^-2 for the emitter diameter d, where the value of γ ranges from 1.62-1.72 depending on d of HBT's used. The 1/f noise model, which rigorously deals with the recombination current at the base surface I_bs as a function of I_b as well as of d is proposed. Applying our noise model to the dependence of SI_b on I_b, as well as on d, reveals that even though γ is less than two, the origin of SI_b is due to the recombination of electrons at the exposed base surface near the emitter edges. On the basis of theoretical considerations for the diffusion length of electrons and traps at the base surface, the Hooge parameter α_H for the noise due to the base surface recombination is deduced to be in the order of 10 ^-2 for the first time     

Low-frequency noise in modern bipolar transistors: impact ofintrinsic transistor and parasitic series resistances

In modern submicrometer transistors, the influence of the internal base and emitter series resistances, on both the I-V characteristics and the LF noise at higher bias currents, becomes important. In this paper expressions are presented for the LF noise in transistors, where the influence of the series resistances has been taken into account. The expressions have been compared with recent experimental results from the literature obtained from modern submicrometer (heterojunction) bipolar transistors. At low forward currents the LF noise in such transistors is determined by spontaneous fluctuations in the base and collector currents. In most transistors at higher forward currents, the parasitic series resistances and their noise become important     

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.     

Design of bipolar imaging devices (BASIS): analysis of random noise

A design methodology for a bipolar imaging device, the base-stored image sensor (BASIS), has been established by theoretical analysis and experimental verification for random noise. The random noise in BASIS is dominated by the shot noise in readout and transient reset operation. The theoretical analysis has been carried out by introducing the probability density functions for these operations. The readout noise depends on the base-to-collector junction capacitance C_bc , the emitter common current gain h_FE, the storage capacitor C_T, and the emitter voltage V _E. The reset noise has been confirmed to be given by thermal noise. The theoretical results coincide well with the experimental results obtained by TEG devices. An expression for the S/N ratio has been derived theoretically. It is found that h_FE should be made as large as possible and ( C_bc+C_be) as small as possible to improve the S/N ratio for random noise, where C _be is the base-to-emitter junction capacitance     

DC, RF, and noise characteristics of carbon-doped base InP/InGaAsheterojunction bipolar transistors

The first successful demonstration of high-performance InP/InGaAs heterojunction bipolar transistors utilizing a highly carbon-doped base is reported. The detailed device characteristics including dc, RF, and noise performance have been investigated. For the first time base layers free of hydrogen passivation have been obtained using chemical beam epitaxy. The HBT's showed almost ideal dc characteristics; a gain independent of collector current, a near unity ideality factor, a very small offset-voltage, and a high breakdown voltage. Devices having two 1.5 μm×15 μm emitter fingers exhibited a maximum f_T of 115 GHz and f_max of 52 GHz. The device also exhibited a minimum noise figure of 3.6 dB and associated gain of 13.2 dB at a collector current level of 2 mA where a f_T of 29 GHz and f_max of 23 GHz were measured. The nearly ideal dc characteristics, excellent speed performance, and RF noise performance demonstrate the great potential of the carbon-doped base InP/InGaAs HBT's     

Temperature coefficient of resolution of lateral bipolarmagnetotransistors

The authors present measurement results of the temperature coefficient (TC) of magnetic field resolution B_min for dual-collector lateral bipolar magnetotransistors (MTs)-over a temperature range 273 K⩽T⩽373 K. For a bandwidth of 500 Hz centered around 750 Hz, the resolution turns out to be 600 nT at room temperature with a TC of +2.3×10^-3/K. With the MT operating in medium injection, there is very little dependence of B _min on bias conditions. In this regime, the correlation (Γ) between collector noise currents is the highest (near unity), where the forward current gain β of the MT is at its maximum. At higher injection levels, a degradation in Γ is observed, possibly due to emitter crowding effects, behaving in a manner similar to β. The degree of coherence appears to be dependent on frequency; Γ is higher at low frequencies where the base 1/f noise predominates and Γ degrades at higher frequencies when white noise levels from the collector epi region become significant     

High-speed, low-noise InGaP/GaAs heterojunction bipolar transistors

We have demonstrated self-aligned InGaP/GaAs heterojunction bipolar transistors (HBT's) with excellent dc, microwave, and noise performance. A 3×10 μm² emitter finger device achieved a cutoff frequency of f_T=66 GHz and a maximum frequency of oscillation of f_max=109 GHz. A minimum noise figure of 1.12 dB and an associated gain of 11 dB were measured at 4 GHz. These results are the highest combined f_T+f_max and the lowest noise figure reported for an InGaP/GaAs HBT and are attributed to material quality and the use of self-aligned base contacts. These data clearly demonstrate the viability of InGaP/GaAs HBT's for high-speed, low-noise circuit applications     

A high-performance InGaAs/InAlAs double-heterojunction bipolartransistor with nonalloyed n+-InAs cap layer on InP(n) grownby molecular beam epitaxy

An InGaAs/InAlAs double-heterojunction bipolar transistor (DHBT) on InP(n) grown by molecular-beam epitaxy (MBE) that exhibits high DC performance is discussed. An n⁺-InAs emitter cap layer was used for nonalloyed contacts in the structure and specific contact resistances of 1.8×10^-7 and 6.0×10^-6 Ω-cm² were measured for the nonalloyed emitter and base contacts, respectively. Since no high-temperature annealing is necessary, excellent contact surface morphology on thinner base devices can easily be obtained. In devices with 50×50-μm² emitter area, common-emitter current gains as high as 1500 were achieved at a collector current density of 2.7×10³ A/cm² . The current gain increased up to 2000 for alloyed devices     

High-current-gain small-offset-voltage In0.49Ga0.51P/GaAs tunneling emitter bipolar transistors grown by gas sourcemolecular beam epitaxy

Different emitter size, self-aligned In_0.49Ga_0.51 P/GaAs tunneling emitter bipolar transistors (TEBTs) grown by gas source molecular beam epitaxy (GSMBE) with 100-Å barrier thickness and 1000-Å p⁺(1×10¹⁹ cm^-3) base have been fabricated and measured at room temperature. A small-signal current gain of 236 and a small common-emitter offset voltage of 40 mV were achieved without any grading. It is found that the emitter size effect on current gain was reduced by the use of a tunnel barrier. The current gain and the offset voltage obtained were the highest and lowest reported values to date, respectively, in InGaP/GaAs system heterojunction bipolar transistors (HBTs) or TEBTs with similar base dopings and thicknesses     

Extraction of emitter and base series resistances of bipolartransistors from a single DC measurement

A new procedure for extracting the emitter and base series resistances of bipolar junction transistors is presented. The parameters are extracted from a single measurement in the forward active region on one transistor test structure with two separate base contacts, making it a simple and attractive tool for bipolar transistor characterization. The procedure comprises two methods for extracting the emitter resistance and two for extracting the base resistance. The choice of method is governed by the amount of current crowding or conductivity modulation present in the intrinsic base region. The new extraction procedure was successfully applied to transistors fabricated in an in-house double polysilicon bipolar transistor process and a commercial 0.8-μm single polysilicon BiCMOS process. We found that the simulated and measured Gummel characteristics are in excellent agreement and the extracted series resistances agree well with those obtained by means of HF measurements. By adding external resistors to the emitter and base and then extracting the series resistances, we verified that the two base contact test structure offers a simple means of separating the influence of emitter and base series resistances on the transistor characteristics     

Optimization of a 0.6 μm, single polysilicon emitter bipolar technology versus narrow emitter effects

A novel 0.6 μm, single polysilicon emitter bipolar technology has been optimized in order to reduce the consequences of narrow emitter effects (NEE) appearing at the laterals of the emitter area. The primary technological mechanisms of these effects have been studied and differentiated for this technology. They have been found to be the polysilicon over-etch into the underlying silicon, the pedestal oxidation, both of them in the area of the extrinsic base implantation, and the extrinsic base lateral diffusion. Designs of experiments techniques have been used in order to study all these technological elements and their effect on the final performance of the transistors. Common emitter current gain variation versus emitter width has been studied by means of test structures and an optimization method is proposed. Lateral diffusion of extrinsic base has been identified as main source of NEE in this technology, which reduces the transistors current gain. Pedestal oxidation has been identified as secondary source of these effects, acting in an opposite way of lateral diffusion increasing the transistors current gain. This opposed effects have been tuned in the technological optimization to minimize the NEE by means of a mutual compensation.     

Low-frequency noise in UHV/CVD epitaxial Si and SiGe bipolartransistors

In this work a comprehensive investigation of low-frequency noise in ultrahigh vacuum/chemical vapor deposition (UHV/CVD) Si and SiGe bipolar transistors is presented. The magnitude of the noise of SiGe transistors is found to be comparable to the Si devices for the identical profile, geometry, and bias. A comparison with different technologies demonstrates that the SiGe devices have excellent noise properties compared to AlGaAs/GaAs heterojunction bipolar transistors (HBT's) and conventional Si bipolar junction transistors (BJT's). Results from different bias configurations show that the 1/f base noise source is dominant in these devices. The combination of a 1/Area dependence on geometry and near quadratic dependence on base current indicates that the 1/f noise sources are homogeneously distributed over the entire emitter area and are probably located at the polysilicon-Si interface. Generation/recombination (Gm) noise and random telegraph signal (RTS) noise was observed in selected Si and SiGe devices. The bias dependence and temperature measurements suggest that these G/R centers are located in the base-emitter space charge region. The activation energies of the G/R traps participating in these noise processes were found to be within 250 meV of the conduction and valence band edges     

Pnp HBT with 66 GHz fmax

The total emitter to collector delay for a Pnp AlGaAs/GaAs HBT has been reduced to 4.8 ps by employing a thin base (325 Å) and collector (2300 Å). Simultaneously, a low base sheet resistance of 170 ohms/square was achieved with tellurium doping. A higher collector doping than is typically used permitted operation at collector current densities in excess of 5×10⁴ A/cm². A single emitter (2×4 μm²) and a single base contact device topology has an f_t and f_max of 33 and 66 GHz, respectively     

Negative base current and impact ionization phenomena inAlGaAs/GaAs HBTs

Impact ionization phenomena in the collector region of AlGaAs/GaAs heterojunction bipolar transistors give rise to base current reduction and reversal. These phenomena can be characterized by extracting the M-1 coefficient, which can be evaluated by measuring base current changes. Measurements of M-1 are affected at low current densities by the presence of the collector-base junction reverse current I_CBO. At high current densities, three effects contribute to lower the measured M-1 value: voltage drops due to collector (R_C) and base (R_B) parasitic resistances, device self-heating, and lowering of the base-collector junction electric field due to mobile carriers. By appropriately choosing the emitter current value, parasitic phenomena are avoided and the behavior of M-1 as a function of the collector-base voltage V_CB in AlGaAs/GaAs HBTs is accurately characterized     

An accurate analysis of noise in rectangular bipolar transistors including current crowding

An accurate analysis of noise in rectangular bipolar transistors is developed from a distributed model using a collective approach and the transport noise theory. In this model, emitter current crowding effect are taken into account and noise behaviour at intermediate and low values of source impedance is precisely described. The structure of teh equivalent lumped circuit is established, and the analytical relationships characterizing its elements in an extended range of current and frequency are given. It is shown that; (a) the active base region must be represented by a nonlinear impedance with a generalized thermal noise source; (b) for low source impedances the equivalent input voltage shot noise generator is higher than predicted by low injection theories. Furthermore it is found that emitter crowding induces a uniform and important decrease in (a) base impedance (b) thermal noise and (c) the correlation between shot noise generators of the equivalent lumped circuit. Finally it appears that classical low injection theories are valid when crowding occurs in transistors biased with high source impedances.