Low-frequency Noise Performance Research Articles

Current-in-Plane GMR Trilayer Head Design for Hard-Disk Drives: Characterization and Extendibility

The current-in-plane giant magnetoresistive (GMR) trilayer readback sensor (CIP-3L), where only one permanent magnet at the back edge of the GMR stack is used to stabilize and bias a dual free layer system, is reviewed. Micromagnetic modeling is employed to show that the design has improved efficiency over abutted junction (ABJ) tunneling magnetoresistive (TMR) head designs. An experimental evaluation of how permanent magnet thickness (PM Th), interlayer exchange coupling (J), and stripe height impact the signal-to-noise ratio, symmetry, and stability of prototype CIP-3L heads is conducted. The study indicates that PM Th >400 nm, J<-0.8 erg/cm2, and a read width to SH aspect ratio of 1:1 to 0.75:1, gives optimal transfer curve performance. A head gimbal assembly spinstand comparison on perpendicular recording media with best-in-class TMR readers shows that although the amplitude of the CIP-3L heads is lower (believed to be process related), the symmetry, stability, and most important, bit-error rate normalized to electrical write width and read width, are comparable. In addition, the CIP-3L design shows better linearity and low-frequency noise performance than TMR heads. The areal density performance of the best CIP-3L heads shows 195 Gb/in2 recording capability and linear densities of 1100 kbpi

The Effect of Single-Halo Doping on the Low-Frequency Noise Performance of Deep Submicrometer MOSFETs

In this letter, the low-frequency noise performance of single-halo (SH) devices is reported, and the physical mechanisms are identified. Experimental results show that, at constant gate overdrive voltages, SH devices show reduced low-frequency noise levels compared to the conventional devices. However, under constant current bias conditions, the noise reduction is less substantial. Low-frequency noise dependence on channel length is also investigated for SH devices based on the electrical measurements and analytical calculations

1/ f noise performance of MOSFETs with HfO 2 and metal gate on Ge-on-insulator substrates

The low frequency (1/ f) noise performance of n- and p-MOSFETs with HfO 2 and TiN–TaN metal gate on GeOI substrates has been investigated. The LF noise spectra are of the 1/ f γ type, with γ>1. The current noise spectral density is typically one decade higher than for silicon counterparts. The behavior of the noise characteristics points to carrier trapping as the prevailing 1/ f noise mechanism. Using a tunneling coefficient α=6.5×10 7 cm −1 for the Ge/HfO 2 system, the extracted volume and surface trap densities are in the range of 1×10 20/cm 3 eV and a few 10 12/cm 2 , respectively. This is of the same order as the interface trap densities, obtained from charge pumping. It is believed that the Ge/interfacial layer (IL) quality could be responsible for the significantly higher trap densities and noise, compared with Si/HfO 2/ TiN–TaN MOSFETs.

Processing aspects in the low-frequency noise of nMOSFETs on strained-silicon substrates

The impact of different processing factors on the low-frequency (LF) noise of nMOSFETs fabricated in strained-silicon (SSi) substrates will be described. It is shown that the use of an SSi substrate can yield improved LF noise performance compared with standard Czochralski silicon material. This is demonstrated for both full-wafer and selective epitaxial SSi material. The lower 1/f noise points to an improved gate oxide quality, i.e., with a lower interface and bulk defect density, and is correlated with the low-field mobility or transconductance of the transistors. At the same time, it will be demonstrated that there exist defect-related LF noise mechanisms, which generally give rise to excess generation-recombination (GR) noise. Associated with this GR noise, a degradation of either the OFF-state leakage current or the mobility (transconductance) of the devices is observed. It is clear that noise is a sensitive parameter to local defectiveness and may be a useful tool for both materials' characterization and the analysis of processing-related device degradation mechanisms.

High-k Gate Stack Engineering and Low Frequency Noise Performance

Gate stack engineering for deep submicron CMOS has been extensively studied, so that high-k dielectrics in combination with metal gate or FUSI electrodes are implemented in research lines. Much effort concentrated on the optimization of gate stacks from a viewpoint of dielectric properties and reliability. Less information is available on the low frequency noise performance of these gate stacks. This review demonstrates the necessity of gate stack engineering for achieving a low 1/f noise performance. The impact of processing parameters, such as thickness of the interfacial layer and the high-k oxide, bulk properties of the high-k layer, post deposition anneals, choice of gate electrode material will be addressed. Such a systematic study forms the basis for noise modeling as for these gate-dielectrics the standard noise models are no longer applicable. The impact on the noise of strain engineering to boost up the carrier mobility is also briefly discussed.

Low-Frequency ( 1 ∕ f ) Noise Performance of n- and p-MOSFETs with Poly- Si ∕ Hf -Based Gate Dielectrics

The low-frequency (LF) noise performance of n- and p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with different Hf-based gate oxides, deposited by metallorganic chemical vapor deposition (MOCVD) on the same interfacial oxide layer and using polysilicon (poly-Si) as a gate material has been investigated. Independent of the gate oxide, the LF noise spectra of n- and p-MOSFETs are predominantly of the type, with the frequency exponent γ close to 1. For nMOSFETs, the noise spectral density of devices is two orders of magnitude higher than for or (silicates), where , most likely due to trapping by defects in the high- layer. For the silicates with different , no significant differences are noticed for n- and p-MOSFETs. It is shown that the noise characteristics behave as can be expected for a number fluctuations mechanism. The extracted volume and surface trap densities are significantly higher for pure than for the devices. In the latter case, trap densities comparable with the values for the reference transistors are obtained. Hooge’s parameter , as an alternative figure of merit, shows that the devices with MOCVD gate dielectric have the noisiest performance, while MOSFETs yield the lowest , even better than for .

High-k Gate Stack Engineering and Low Frequency Noise Performance

not Available.

1∕ f noise in all-epitaxial metal-semiconductor diodes

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, molecular beam epitaxy (MBE)-grown ErAs:InAlGaAs heterojunctions have recently been shown to provide highly “engineerable” electrical rectification characteristics through the tuning of the Schottky barrier height, while maintaining the very low specific capacitance. This letter reports an approximate 10× improvement in the low-frequency noise performance by using MBE-grown ErAs as the Schottky contact instead of evaporated aluminum. The low-frequency noise power spectrum of ErAs devices has been observed to have a 1∕f1.0 frequency dependence. Constant-current bias-dependent measurements have shown a 1.8 power law dependence of the noise spectral density on dc current.

Low-Frequency Noise Performance of HfO2-Based Gate Stacks

The low-frequency noise characteristics of -based dielectrics have been investigated. Attention is given to the deposition technique (metal oxide chemical vapor deposition or atomic layer deposition) used, the film thickness, and the use of a interface layer. n-Type metal oxide semiconductor devices with equivalent oxide thicknesses (EOTs) of 1.5, 2, 3, and 5.5 nm were studied. It is shown that the LF noise of such high- transistors is like. The behavior of the normalized current spectral density vs the drain current points out that for relative thin interfacial layers and at high gate voltages carrier trapping in the layer governs the current fluctuations. The trap densities extracted from the noise are up to 200 times higher than in a thermal oxide reference wafer (5.5 nm EOT). The deposition technique has no strong impact on the density of traps in the high- layer, which is in the range of . However, a strong difference was observed in the noise contribution, which is dominated by carrier scattering at charged traps. For , the scattering coefficient derived from the noise is smaller than for , which can be interpreted in terms of the suppression of the coulomb scattering by the high dielectric constant.

MOCVD growth of group III nitrides for high power, high frequency applications

This paper reports on the LP-MOCVD growth optimisation of bulk GaN, GaAlN materials and GaAlN/GaN heterostructures grown on Sapphire and Silicon Carbide substrates for MESFET and HEMT applications, and on the device performances obtained with these structures. High purity and high resistivity GaN grown on sapphire and Silicon Carbide has been obtained. GaN/Al2O3 MESFETs based on such high purity GaN buffer layers, have exhibited very promising static and microwave performances: high beakdown voltage ∼200 V, ft = 12 GHz, fmax = 25 GHz and CW output power in excess of 2.2 W/mm at 2 GHz.. They have shown the best low frequency noise performances, with the lowest Hooge's parameter as compared to previous values reported in the literature for different GaN-based FETs (HFETs and HEMTs). The main mechanisms involved in the growth of GaAlN/GaN alloys have been studied and their impact on the physical properties of these materials determined. A parasitic reaction was clearly identified to occur in the gas phase between TMA and NH3, with a strong influence on the growth rate and the aluminium incorporation. The SiC substrate surface preparation (both ex-situ and in-situ) and the nucleation layer growth conditions (growth temperature, thickness, composition and strain) have been found to be key steps of the GaAlN/GaN/SiC growth process. Static characteristics of the devices such as maximum drain current Idss or pinch-off voltage have been correlated with the nucleation layer composition of the HEMT structure and the defect density of the SiC substrate. The devices performances related to our first GaAlN/GaN HEMT structures grown on Sapphire and Silicon Carbide have confirmed the high potentiality of GaN and related alloys for high power microwave transistors. Load-Pull measurements performed at 2 GHz on devices related to GaAlN/GaN/Al2O3 HEMT structures, have shown a remarkably high output power density (4.4 W/mm) and absolute power level (3.2 W for 1 mm devices). These power level results for devices on sapphire substrates measured on wafer, are well in agreement with the international state of the art. Nevertheless, the thermal effects, which lead to a significant reduction of the power density with the increase of the transistor size, have been found to be more pronounced for devices on sapphire. In order to improve the thermal properties of HEMT's material, the growth process of GaAlN/GaN HEMTs was transferred onto Silicon Carbide substrates. Devices related to GaAlN/GaN/SiC HEMT structures have been measured at 10 GHz using a load pull system. They exhibited a CW output power in excess of 6.2 W/mm for a gate length of 0.25 µm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Strained Si HFETs for microwave applications: state-of-the-art and further approaches

This paper reviews the RF and noise performance of strained Si heterostructure field-effect transistors. For SiGe n-HFETs the high RF figures of merit f T=90 GHz, f MAX=188 GHz and noise performance NF MIN =0.3 dB at 2.5 GHz demonstrate the capabilities of these devices for microwave circuit applications. Recently some IC demonstrators have been successfully implemented. Strained Si HFETs fabricated on thick SiGe virtual substrates have been traditionally employed as a vehicle of study. Nevertheless these thick relaxed buffers involve some decisive disadvantages: Reduction of the wafer throughput, non-acceptable surface topology if implemented in mixed technologies like CMOS, and, in particular, self-heating due to low thermal conductivity of SiGe alloys compared to Si. In order to overcome these drawbacks several approaches to reduce the buffer thickness have been very recently developed. In this paper the RF and low frequency noise performance of SiGe HFETs prepared on very thin virtual substrates are reported. The potentialities of these technologies have not yet reached their limits. One can expect a great improvement by combining a proper device shrinking with very thin virtual substrates. These heterosystems could become the backbone of strained silicon devices towards microwave applications.

Effects of body biasing on the low frequency noise of MOSFETs from a 130 nm CMOS technology

The impact of body biasing on the low frequency noise (LFN) performances of MOS transistors from a 130 nm CMOS technology was investigated. The body-to-source voltage VBS was varied from –0.5 V to +0.5 V for reverse and forward mode substrate biasing. Detailed electrical characterisation was performed and the benefits of the body bias analysed in terms of current and maximum transconductance variations. Noise measurements were first performed at low drain bias VDS=±25 mV and VBS=0 V in order to discuss the noise origin in the devices. Results are in agreement with the carrier number fluctuation theory ΔN for NMOS and with the correlated carrier number–mobility ΔN–Δμ model for PMOS. Bulk bias dependence of the LFN was investigated at VDS=VDD=±1.2 V. Significant noise reduction of about 50% in both N and PMOSFETS was observed in the weak inversion regime when applying a forward body bias. In strong inversion, the noise level was found to be approximately independent of the substrate bias VBS. An explanation of the main noise results based on McWhorter&apos;s number fluctuation theory is proposed.

Effect of the surface and barrier defects on the AlGaN/GaN HEMT low-frequency noise performance

We report on the effect of Si/sub 3/N/sub 4/ passivation of the surface of AlGaN/GaN transistors on low-frequency noise performance. Low-frequency noise measurements were performed on the device before and after the passivation by a Si/sub 3/N/sub 4/ film. A lower level of the low-frequency noise was observed from the device after the passivation. The passivation layer improved high-frequency, large-signal device performance, but introduced parasitic leakage current from the gate. A lower level of flicker noise is explained by the fact that noise is mostly originated from the fluctuation of sheet charge and mobility in the ungated region of the device due to the defects on the surface and in the barrier of the unpassivated device. Passivation eliminates part of the defects and higher leakage current increases the number of electrons on the surface and in the vicinity of the barrier defects, lowering the contribution to the low-frequency noise according to Hooge's law.

Noise analysis of correlated double sampling sc integrators with a hold capacitor

Noise performance of the correlated double sampling switched-capacitor integrators incorporating a supplementary hold capacitor is analyzed. These types of integrators rely on an extra capacitor to attenuate the amplifier low-frequency noise. Approximate expressions for the input-referred noise of the integrators are derived. It is shown that a large parasitic capacitance at the amplifier input may seriously degrade the low-frequency noise performance of such structures.

Dynamic and low-frequency noise characterization of Si-Ge heterojunction-bipolar transistors at cryogenic temperatures

We present the characterization of the static and low-frequency noise performances of some commercial Si-Ge heterojunction bipolar transistors from 4.2 K to room temperature. The low injection region of operation was considered in view of their possible applications for the readout of array of cryogenic detectors.

Comprehensive noise performance of ultrathin oxide MOSFETs at low frequencies

An analytical model and analysis of the low frequency noise performance of ultrathin oxide MOSFETs are presented. The model includes the effects of gate tunneling leakage current, low frequency noise sources, and their cross correlation coefficient between the input and the output. The correlation coefficient is not negligible in the existence of direct tunneling current through the gate oxide, and has an impact on the overall noise performance at low frequencies. Based on the partition noise theory and BSIM4 gate leakage current model with the source–drain partition, the correlation coefficient is obtained from a physical and rigorous modeling of intrinsic noise sources. The calculated results are compared with correlation noise measurements and good agreement is observed. An analytical formulation of low frequency noise performance is newly derived using the frequency-dependent noise parameters P LF, R LF, and C LF. The noise performance parameters, such as minimum noise figure, optimum source resistance and reactance, are graphically presented to accurately predict the influence of the gate leakage current on the low frequency noise performance. From quantitative results simulated with typical device parameters, it is shown that the proposed model can be used for optimum design of ultrathin oxide MOS devices and circuits at low frequencies.

Critical spacing between emitter and base in InGaP heterojunction bipolar transistors (HBTs)

In this paper, the influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 /spl mu/m without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6/spl sim/0.8 /spl mu/m between the emitter and the base of an InGaP HBT is required.

Low-frequency noise analysis of Si/SiGe channel pMOSFETs

Low-frequency noise characteristics of 0.1 μm Si 1− x Ge x channel pMOSFETs were studied by numerical simulations in the framework of the carrier number fluctuation model as well as the correlated fluctuation in the mobility model. Simulation results predict that Si 1− x Ge x channel pMOSFETs could offer improved low-frequency noise performance as compared to the conventional bulk Si devices. This improvement in Si 1− x Ge x channel pMOSFETs could be attributed to less effective oxide trap density for noise generation due to the increasing separation of quasi-Fermi level and valence band edge at Si–SiO 2 interface by Ge-induced band offset.

Investigations on the low-power and low-frequency noise performance of pHEMT at 4.2 K

Pseudomorphic GaAs HEMTs with a gate length of 1μm have been realized and characterized at 4.2K. For the device with a gate width of 4mm, a gate leakage current less than 1pA and a total input capacitance lower than 10pF have been obtained for any practical bias conditions. The channel resistance can be modified more than 10 9 times with a gate bias variation less than a half volt. An intrinsic voltage gain higher than 10 can be reached with a power dissipation equal to or less than 0.15mW. Under this power supply condition, equivalent input noise voltages of 8.4, 3.2 and down to 1.3nV/√Hz can be obtained at frequencies of 1, 10 and 100kHz respectively. This noise voltage has been studied as a function of the drain current. Finally, the experimental results of this work have shown that the device's noise voltage can be linked to its DC parameters.

Effect of forward and reverse substrate biasing on low-frequency noise in silicon PMOSFETs

Forward body biasing improves the low-frequency noise performance of p-channel metal-oxide semiconductor (PMOS) transistors by about 8 dB/V. Therefore, for analog design, forward body biasing may be preferred if noise is a concern. This is in agreement with the improvement of other MOSFET parameters such as the decrease of the threshold voltage (V/sub T/) or the increase of unity current-gain frequency (f/sub T/) on forward substrate- (or body)-source biasing (V/sub BS/). Also, forward V/sub BS/ is very attractive for low voltage supply (V/sub DD/<0.6 V) and low-power, low-noise circuits. A detailed analysis of the dependence of the noise level on VBS and on the gate-source (V/sub GS/) biasing showed that the dependence on V/sub BS/ seems to be smaller in weak inversion, and it increases in strong inversion. The dependence on V/sub GS/ has a turning point at V/sub GS//spl ap/0.8 V, independent of body bias, which it seems is due to the activation of oxide traps, as the noise waveform showed a random telegraph signal (RTS) component at V/sub GS/>0.8 V. Generally, it is confirmed that the spectral density S/sub I/ of the total low-frequency noise of the drain current I/sub D/ is proportional to the square of I/sub D/, i.e., S/sub I//spl prop/I/sub D//sup 2/, but it cannot be clearly ascribed to either number fluctuation or mobility fluctuation models. In addition, both models cannot accurately describe the dependence of the noise level on the body bias.