Low-frequency Noise Properties Research Articles

Shot noise of coupled semiconductor quantum dots

The low-frequency shot noise properties of two electrostatically coupled semiconductor quantum dot states which are connected to emitter/collector contacts are studied. A master equation approach is used to analyze the bias voltage dependence of the Fano factor as a measure of temporal correlations in tunneling current caused by Pauli's exclusion principle and the Coulomb interaction. In particular, the influence of the Coulomb interaction on the shot noise behavior is discussed in detail and predictions for future experiments will be given. Furthermore, we propose a mechanism for negative differential conductance and investigate the related super-Poissonian shot noise.

Temperature dependence of the low-frequency noise properties in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ intrinsic Josephson junctions

We have measured the temperature dependence of the low-frequency noise properties across for mesa stacks of intrinsic Josephson junctions (IJJs) in single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (BSCCO) in the absence of an external magnetic field. The measured curves for noise spectrum density S/sub V/(f) showed a 1/f frequency dependence at temperatures in the range from 4.3 K to 150 K except 36 K. We estimated the magnitude of the S/sub V/(f) by using Rogers and Buhrman's empirical theory and Machlup's formula. From the observed curves for S/sub V/(f), we estimated a 1/f noise level /spl eta/ for a BSCCO IJJ biased at a sub-gap voltage of approximately 10/sup -5/ /spl mu/m/sup 2/, and this value was almost completely independent of temperature in the range between 4.3 K and 40 K. We also found that the /spl eta/ values above T/sub c/ were smaller by a factor of approximately 10 than those below T/sub c/. The /spl eta/ value for the BSCCO IJJ is approximately two orders of magnitude greater than for an epitaxial NbN/MgO/NbN tunnel junction biased above-gap voltage. We consider that the observed variation in the noise level with temperature is not interpretable in terms of a magnetic origin and the 1/f noise in a BSCCO IJJ may be somehow associated with stress or defects in the BiO and/or SrO layers act as tunnel barriers.

Topology investigation for the low frequency noise compact modelling of bipolar transistors

The low frequency noise (LFN) properties of bipolar transistors are investigated in terms of equivalent input referred, partially correlated noise generators. These properties are studied as a function of the intrinsic noise sources and of the small-signal model topology. Topology invariance and identity properties are identified and their practical implications on the LFN modelling of bipolar transistors are assessed.

Has SiGe lowered the noise in transistors?

It is shown that low-frequency noise (LFN) in SiGe-base HBTs and SiGe-channel pMOSFETs can be made significantly lower than it is in their all-Si counterparts. The noise reduction in the HBTs results principally from the elimination of the emitter/base interfacial oxide, which, in the Si bipolar junction transistors, serves to boost the current gain. A reduction in the LFN in the SiGe channel pMOSFETs is also possible, but requires a careful design of the structure, as the power spectral density (PSD) of drain current fluctuations is often a non-monotonic function of their structure parameters. Optimisation of the LFN requires a simulation of the PSD. This can be done using an analytical model assuming (i) carrier-number fluctuation noise generation by trapping/release of charges at the SiO2/Si interface, resulting in correlated fluctuations in the retrograded SiGe channel and in the SiO2/Si interface channel, and (ii) mobility fluctuations in each channel. The quality of the SiO2/Si interface is crucial for the overall LFN properties of the MOSFETs, as it is responsible for the number fluctuation noise which is predominant in the range of currents commonly used.

1/f noise of Bi2Sr2CaCu2Oy intrinsic Josephson junctions

We have measured the low-frequency voltage noise properties across mesa stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2Oy (BSCCO) single crystals as a function of bias voltage. The BSCCO mesas with area of 160×40 μm2 were fabricated on the surface of cleaved BSCCO single crystals using standard photolithography and Ar ion-milling techniques. The measured noise voltage spectrum density SV(f ) had a 1/f dependence on frequency. The magnitude of the 1/f noise spectra was found to increase monotonically with the branch number in the I–V characteristic at fixed bias current, and no anomalously enhanced 1/f noise was observed.

Low frequency noise and reliability properties pf 0.12 μm CMOS devices with Ta 2O 5 as gate dielectrics

Low frequency noise and reliability properties pf 0.12 μm CMOS devices with Ta 2O 5 as gate dielectrics

Random telegraph voltage noise in a Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ intrinsic Josephson junction

Low frequency noise properties have been investigated in mesa-type Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO) intrinsic Josephson junction. The junction area for this mesa was 160 /spl mu/m/spl times/40 /spl mu/m. The mesa showed highly hysteretic current-voltage characteristic at low temperatures, and had seven discrete-resistive-branches. For the noise measurements only at T/spl sim/36 K, we observed a rapid increase in the noise voltage spectrum over our entire bandwidth. Large random telegraph voltage noises (RTVN) were only detected for low bias current region of the BSCCO mesa for current biased on the 4th (I/sub b/=6.0 mA) and 5th (I/sub b/=5.0 mA) resistive-branches, and also not observed for all of voltage region at 4.2 K and low bias voltage region, from 1st to 3rd resistive-branches, at 36 K. The measured S/sub v/(f) had the Lorentzian frequency dependence, as expected from the Machlup formula for random telegraph signal. The possible origin of the large RTVN may be thermal fluctuation of the "switchback" voltage V/sub min/.

Low-frequency noise in polymer transistors

The low-frequency noise (LFN) properties of field-effect transistors (FETs) using polymers as the semiconducting substrate material are investigated and explained in terms of the nonstationary mobility /spl mu/ in the semiconducting polymer. In the frequency (f) range f<1 kHz it was found that 1/f noise prevails over other types of LFN in these polymer FETs (PFETs). The spectral density S/sub I/ of LFN of the drain current ID is proportional to the DC power V/sub DS//spl middot/I/sub D/ applied to the PFETs channel, from the ohmic to the saturation modes of device operation. In addition, S/sub I/ is affected by the carrier mobility /spl mu/ in PFETs channel, as /spl mu/ in organic FETs is dependent on the biasing. Thus, SI can have an additional sensitivity to I/sub D/, that is, S/sub I//spl prop/(V/sub DS//spl middot/I/sub D/)/sup 1-k/, where k/spl sim/0.1. In general, the 1/f LFN of PFETs follows the relations that have been obtained for crystal and inorganic FETs with minor correction for nonstationary mobility /spl mu/.

Effect of starting SOI material quality on low-frequency noise characteristics in partially depleted floating-body SOI MOSFETs

The low-frequency noise properties of partially-depleted (PD) floating-body silicon-on-insulator (SOI) MOSFETs fabricated on two types of commercially available bonded SOI (BSOI) wafers were experimentally investigated. In the pre-kink region, a drain bias dependent Lorentzian-like noise has been observed for UNIBOND wafers, while a pure 1/f noise has been achieved for ELTRAN wafers. Our analysis shows that the charge fluctuation induced by emission process through intermediate-level centers in the drain-depletion region causes the instability in the body voltage, resulting in the pre-kink excess noise for UNIBOND wafers.

RTS noise in submicron SiGe epitaxial base bipolar transistors

In this paper, we report a comprehensive study of Random Telegraph Signal (RTS) noise in SiGe epitaxial base bipolar transistors. We analyse the multilevel fluctuations of base and emitter forward currents before and after reverse stress on the emitter-base junction. We show the influence of the chemical treatment preceeding polysilicon emitter deposition on noise properties. We identified that RTS noise arises from different regions in the device : the silicon/polysilicon interface if an oxidizing surface preparation is used, and the emitter periphery after stress-induced degradation. Temperature and bias dependent measurements allowed us to characterize these defects (activation energy, defect type), to analyse their impact to the low frequency noise properties of these transistors and to discuss the role of hot carrier stressing.

Electrical and low frequency noise properties of Gd and GdCo silicidecontacts on n-type Si

Gd and GdCo layers were evaporated onto n-type silicon and silicideswere formed by in situ annealing at 400 and 700 °C. Theelectrical properties of the resulting Schottky diodes were investigated bycurrent-voltage, capacitance-voltage and low frequency noise measurements.The Gd/Si contacts show an ohmic behaviour for both annealing temperatures,while the GdCo/Si contacts show a rectifying behaviour with a high(~0.65 eV) and a low (~0.52 eV) Schottky barrierheight for the annealing temperatures of 400 and 700 °C,respectively. It was found that Co retards the Gd-Si reaction and reduces thedensity of the donor-type point defects generated within the silicon substrateduring the Gd silicidation process.

Flicker noise properties of organic thin-film transistors

The low frequency noise properties of organic thin film transistors are studied here as a function of frequency and bias. Various n-channel and p-channel devices were evaluated and found to exhibit 1/f-type of noise in the 1 Hz–10 kHz range. The drain current noise is found to vary proportionally with drain current. The noise level is comparable to that found in Si metal–oxide–semiconductor field-effect transistors within the operation region of the devices, owing to the smaller drain currents in organic transistors, although the intrinsic noise is considerably higher in the organic transistors. The viability of using the organic materials in low noise circuits is demonstrated by a ring oscillator.

Low frequency noise behaviour of InP/InGaAs heterojunction bipolar waveguide phototransistors

In this paper we report on both the DC and low frequency noise (LFN) properties of InP/InGaAs heterojunction bipolar phototransistors (HPTs) featuring waveguide type illumination. Both DC and LFN measurements demonstrate the good quality of these devices. In particular, they exhibit a 1/ f noise figure-of-merit of 2·10 −8 μm 2, which is exceptionally very good in the field of the compound semiconductor HBTs, where values around 10 −7 μm 2 are usually reported.

Low-frequency noise properties of dynamic-threshold (DT) MOSFET's

This paper shows that MOSFET operated in dynamic-threshold (DT) mode (V/sub body/=V/sub gate/) is more suitable for low-noise RF/analog applications than those operated in conventional mode (V/sub body/=V/sub source/). Detailed low-frequency noise properties of these two modes of device operation were compared for 0.31-μm gate MOSFET's, in which NMOS's are surface-channel devices (S.C.) and PMOS's are buried-channel (B.C.) devices. Experimental data show that when the devices are biased at same transconductance, the low-frequency noise in DT mode is 30 times lower (at g/sub m/=2.2×10/sup -3/ S) than that in the conventional mode for the B.C. devices and ten times (at g/sub m/=2.0×10/sup -3/ S) lower for the S.C. devices.

Low-frequency noise in field-cooled, directly coupled magnetometers

We have studied the low-frequency noise properties of high-T/sub c/ directly coupled magnetometers involving dc Superconducting Quantum Interference Devices (SQUIDs) connected to four different types of pickup loop. Two of the pickup loops have a solid-washer design, while the other two comprise structures with narrow (4 /spl mu/m) linewidths. The devices were fabricated from YBCO thin films laser deposited on bicrystal substrate. The noise properties of the magnetometers cooled and maintained in static magnetic fields were measured at 77 K. The pickup loop contributes to the 1/f noise of field-cooled devices solely through vortex motion at tapered outer edges; this noise was eliminated by repatterning the edges to make them sharp. We demonstrate that solid-film washers can be replaced with narrow-linewidth structures without any loss in effective area.

High-temperature superconducting YBCO dc SQUID gradiometers fabricated on STO bicrystal substrates

HTS dc gradiometers have been fabricated with slots and flux dams in their SQUID washers. Using a single layer of YBCO, the gradient sensitivity is limited by the sensing magnetometer in the centre of the structure. The spatial response of such devices has been measured experimentally indicating that single layer devices, in terms of gradient sensitivity, have characteristics that deviate slightly from idealized first order gradiometers. The flux noise of these devices is discussed with particular emphasis on their unshielded low frequency noise properties. We also discuss the effect of different cooldown procedures on the flux noise.

Low-frequency noise properties of selectively dry etched InP HEMT's

The low-frequency noise of lattice-matched InAlAs/InGaAs/InP high electron mobility transistors (HEMT's) gate recess etched with a highly selective dry etching process and with conventional wet etching were studied at different gate and drain biases for the temperature range of 77-340 K. The measurements showed a significantly lower normalized drain current 1/f noise for the dry etched HEMT's under all bias conditions. No difference in the normalized gate current 1/f noise could be observed for the two device types. By varying the temperature, four electron traps could be identified in the drain current noise spectra for both dry and wet etched devices. No additional traps were introduced by the dry etching step. The concentration of the main trap in the Schottky layer is one order of magnitude lower for the dry etched HEMT's. No hydrogen passivation of the shallow donors was observed in these devices. We presume hydrogen passivation of the deep levels as the cause for the trap density reduction. The kink effect in the dry etched HEMT's was observed to be reduced significantly compared with wet etched devices which gives further evidence of trap passivation during dry etching. These results show that dry etched InP HEMT's have suitable characteristics for the fabrication of devices for noise sensitive applications.

Low-frequency noise properties of SiGe HBT's and application to ultra-low phase-noise oscillators

This paper presents an extensive electrical characterization of Si/SiGe/Si heterojunction bipolar transistors (HBT's) grown by molecular beam epitaxy (MBE). These devices are designed for microwave and millimeter-wave applications since they present a maximum oscillation frequency in the 40-GHz range. The processing technology, featuring a high-quality oxide passivation, results in ideal Gummel plots and an input noise corner frequency of 250 Hz at lowest. A dielectric resonator oscillator (DRO) at 4.7 GHz has, therefore, been realized. The measured phase-noise level of this oscillator is below -135 dBc/Hz at 10-kHz offset frequency, which is at least 10 dB better than the best FET or HBT state-of-the-art DRO's.

Saturation of 1/f noise level of superconductor-constrictions-superconductor mesoscopic devices

Low frequency noise properties of all-thin film superconductor-constrictions-superconductor devices have been investigated. We first found that the magnitude of 1/f noise level rapidly decreases with increasing the device quality factor Q−1 and saturates for Q−1≥2. From Hooge theory [1] this saturation phenomena indicates that the number of carriers in the system no longer changes for Q−1≥2.

Crossover of Noise Power from Thermal to Shot Noise in Superconducting Mesoscopic Devices

Low-frequency noise properties of all-thin-film superconducting Nb-(constrictions)-NbN point contacts have been investigated. This type of contact can be regarded as a superconducting mesoscopic system, and its quasiparticle characteristic can be analyzed effectively Blonder, Tinkham and Klapwijk ( BTK) theory based on the Bogoliubov-de Gennes equation. We also discuss on white noise in Nb-(constrictions)-NbN point contacts, in the clean and ballistic limit. The temperature dependence of crossover voltages between thermal noise and shot noise in the ballistic system is in good agreement with calculated values.