Contribution To Leakage Current Research Articles

Recovery of drain-induced threshold voltage shift by positive gate bias in GaN power HEMTs with p-GaN gate

We demonstrate that exposure to positive gate bias can favor a fast recovery of the threshold voltage variation induced by off-state stress, in p-GaN gate high electron mobility transistors. Two process splits were investigated, having different Schottky barriers at the metal/p-GaN junction. Results indicate that: (a) drain stress may result in significant threshold voltage increase; (b) devices with sufficiently high gate leakage current show an immediate recovery after gate turn-on, resulting in stable operation in actual applications. The contribution of leakage current is demonstrated, based on recovery experiments at different voltages and for the same rate of hole injection from the gate.

Investigation and passivation of boron and hydrogen impurities in tetragonal ZrO2 dielectrics for dynamic random access memory capacitors

Tetragonal ZrO2 high-k material as the dielectric layer of dynamic random access memory (DRAM) capacitors faces bulk defect related leakage current, which is one of the main obstacles to the down-scaling of DRAM devices. Boron and hydrogen impurities are known to be responsible for leakage current degradation and are hard to be removed in DRAM capacitors. However, the defect origins of boron and hydrogen leakage current are still puzzling, and corresponding suppression methods are urged. In this work, the properties of boron and hydrogen impurities in tetragonal ZrO2 are investigated using first-principles calculations, and defect types such as boron and hydrogen interstitials are discovered to have detrimental defect levels related to leakage current. Based on the discovery, a chlorine co-doping approach that can passivate detrimental defects by forming defect complexes is further proposed. By introducing level repulsion due to coupling between defect states, defect levels of passivated defect complexes are moved out of the region of leakage current contribution. Thus, bulk defect related leakage current in tetragonal ZrO2 based DRAM capacitors can be effectively suppressed without device structure modification, and a broad vista is opened for next-generation DRAM devices.

Selective Epitaxial Growth of In Situ Doped SiGe on Bulk Ge for p+/n Junction Formation

Epitaxial in situ doped Si0.73Ge0.27 alloys were grown selectively on patterned bulk Ge and bulk Si wafers. Si0.73Ge0.27 layers with a surface roughness of less than 3 nm were demonstrated. Selectively grown p+Si0.73Ge0.27 layers exhibited a resistivity of 3.5 mΩcm at a dopant concentration of 2.5 × 1019 boron atoms/cm3. P+/n diodes were fabricated by selectively growing p+- Si0.73Ge0.27 on n-doped bulk Ge and n-doped Si wafers, respectively. The geometrical leakage current contribution shifts from the perimeter to the bulk as the diode sizes increase. Extracted near midgap activation energies are similar to p+/n Ge junctions formed by ion implantation. This indicates that the reverse leakage current in p+/n Ge diodes fabricated with various doping methods, could originate from the same trap-assisted mechanism. Working p+/n diodes on Ge bulk substrates displayed a reverse current density as low as 2.2·10−2 A/cm2 which was found to be comparable to other literature data. The layers developed in this work can be used as an alternative method to form p+/n junctions on Ge substrates, showing comparable junction leakage results to ion implantation approaches.

Enhanced ferroelectricity in relaxor $$\hbox {0.7BiFeO}_{{3}}{-}0.3(\hbox {Ba}_{0.85}\hbox {Ca}_{0.15})\hbox {TiO}_{{3}}$$ ceramics using ball milling technique

$$\hbox {0.7BiFeO}_{{3}}{-}0.3(\hbox {Ba}_{0.85}\hbox {Ca}_{0.15})\hbox {TiO}_{{3}}$$ (BF–BCT) ceramics were synthesized with a conventional solid-state reaction method. The electrical properties of the BF–BCT ceramics depend on the milling time via a planetary ball-milling technique. The results show that the sample prepared by milling for 40 h possesses a rather large remanent polarization of $$52 \,\upmu \hbox {C}/\hbox {cm}^{2}$$ and this value is superior to that of Non-Pb BF-based ceramics at room temperature. Moreover, the values of remanent polarization were confirmed by a PUND measurement to eliminate the contribution of leakage current. We attributed the large remanent polarization to the decrease in oxygen vacancies confirmed by X-ray photoelectron spectroscopy results. Moreover, the BF–BCT ceramics exhibit the dielectric relaxation process caused by the diffusion of oxygen vacancies inside ceramics.

Effect of domain switching contribution on polarization current, leakage current and switching charge density studied by PUND method in (Ba1−x,Cax)TiO3 ceramics

The present study illustrates the effect of domain switching on polarization current and leakage current in (Ba1−xCax)TiO3 (0 ≤ x ≤ 0.4) lead-free ceramics prepared by sol-gel method. The influence of Ca2+ concentration on the structural, microstructure and dielectric properties of BaTiO3 (BT) was investigated. The study shows that domain switching has a significant effect on polarization current and switching leakage current behavior. Un-switching leakage current was observed to be lower than the switching leakage current in whole range of electric field due to restrict the space charges contribution in the absent of domain switching effect. The highest polarization current and lowest leakage current were achieved in the composition x = 0.2. Effect of frequency into polarization current has been introduced, where the current peak increased and shifted to higher electric field by increasing the applied frequency due to the high rate change of electric field corresponding domain switching rate. The difference between remnant polarization estimated by P-E loop and Positive Up Negative Down (PUND) methods has been highlighted. The results show that the remnant polarization appraised by PUND method is lower than the value estimated by P-E loop due to absence of the leakage current contribution.

Enhancement of switching/un-switching leakage current and ferroelectric properties appraised by PUND method of (Ba1-xCax)TiO3 lead free piezoelectric near MPB

Lead free perovskite (Ba1-xCax)TiO3 (BCT) (0 < x ≤ 0.4) ceramics were successfully prepared by Sol gel technique in lower thermal processing conditions than the solid solution method. The samples were calcined at 1000 °C/and they were sintered at 1200 °C. The structure, dielectric, leakage current and ferro-piezoelectric properties of perovskite (Ba1-xCax)TiO3 (0 < x < 0.4) were investigated. In Ca-doping range 0 < x < 0.3, pure single phase of BCT has been detected. Secondary phase of CaTiO3 has been detected for x = 0.4. The addition of Ca2+ has a negligible effect on the Curie temperature but it inhibits the grain dwindle. High permittivity and low dielectric loss values were achieved in the sample (Ba0.8Ca0.2)TiO3 due to Morphotropic Phase Boundary (MPB) coexistence. Anomalous switching leakage peak (∼2 kV/cm) was observed due to the domain switching. The (Ba0.8Ca0.2)TiO3 exhibits low leakage even in the absence of the electric field (Joff = 1.5368e−13 A/cm2), due to the enhancement of the microstructure properties. The Ferroelectric properties were estimated by P-E loop and Positive Up Negative Down (PUND) methods and the results are shown the remnant polarization estimated by P-E loop is almost back to leakage current contribution. Piezoelectric properties were enhanced in (Ba0.8Ca0.2)TiO3 (d∗33 = 498 pm/v) due to BT-CT phases coexistence.

Room temperature multiferrocity and magnetodielectric properties of ternary (1-x) (0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xBiFeO3 (0 ≤x≤ 0.9) solid solutions

(1–x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xBiFeO3 (0 ≤x≤ 0.9) ternary ceramics were prepared by the modified Pechini method. X ray diffraction patterns manifest that the samples undergo a gradual structural transformation from the rhombohedral-tetragonal morphotropic phase boundary to the rhombohedral phase with the increasing content of BiFeO3. Room temperature ferromagnetism was observed in BiFeO3-rich samples with x ≥ 0.6, and this ferromagnetism can be ascribed to the suppression of the spiral spin structure with the canting of antiferromagnetically ordered spins. The BiFeO3-rich samples (x = 0.6–0.8) exhibit superior ferroelectric properties with the maximum remanent polarization of 44.7 μC/cm2, as confirmed by the positive-up negative-down measurement to exclude the contribution of leakage current. The coexistence of room-temperature ferromagnetism and ferroelectricity manifests that the lead-free BiFeO3-based solid solutions are quite promising multiferroic materials and may be important for potential applications in BFO-based magnetoelectric devices.

Large remanent polarization and enhanced magnetic properties in non-quenched Bi(Fe,Ga)O3-(Ba,Ca)(Zr,Ti)O3 multiferroic ceramics

It is a tough issue to release the underlying polarization and magnetization simultaneously in non-quenched polycrystalline BiFeO3 ceramics due to their high conductivity, intensive domain-wall clamping, and long range spiral spin arrangement. Here, 0.75BiFe0.98Ga0.02O3-0.25(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 multiferroic ceramics were fabricated by a conventional solid-state reaction with a non-quenched method. The crystalline structure analysis revealed that the ceramics showed a rhombohedral (R3c) perovskite structure. Superior ferroelectricity was observed in the ceramics with high remanent polarization (44 μC/cm2), which has been re-verified by PUND measurement to exclude the contribution of leakage current. Moreover, enhanced ferromagnetism with remanent magnetization (0.20 emu/g) was also obtained at 300 K. We have demonstrated that the observed macroscopic magnetization was attributed to the canting of the spins due to melting away of the spiral structure rather than other Fe-containing impurity phases. The excellent ferroelectric and ferromagnetic performance suggests that this non-quenched lead-free BiFeO3-based ceramics are quite promising multiferroic materials.

An improved energy efficient SRAM cell for access over a wide frequency range

Leakage current contribution to the power consumption cannot be ignored in the sub-100nm technology. Drastic reduction of channel length of the modern highly scaled device enhances the leakage current significantly. Two novel 8T-SRAM cells low-leakage-current SRAM cell (LLC-SRAM cell) and low-leakage-current high-threshold-voltage SRAM cell (LLC-HVT SRAM cell) are proposed to offer high energy efficiency. The cell performances are compared with 8T NC-SRAM cell and 6T-SRAM cell. The proposed cells significantly reduce the overall power consumption. The cell array simulations are performed in spectre with a general purpose 45nm technology library. The short-circuit current reduction during state transition helps to decrease the dynamic power consumption. In standby mode the cell operates at a voltage lower than the supply which brings down the leakage current and hence leakage power. Besides the energy prospective the stability, speed and writ-ability analysis are also performed in this work.

(Invited) On the Electrical Activity of Extended Defects in High-Mobility Channel Materials

The electrical activity of extended defects (dislocations; antiphase boundaries;...) in high-mobility channel materials (strained-Si; (strained)-Ge, GaAs and InGaAs) is investigated by means of simple device structures (p-n diodes and MOS capacitors). These are fabricated in substrates with a well-controlled density of predominant extended defects, enabling the determination of a specific leakage current contribution per defect. It is shown that there is a linear relationship between the area leakage current density and the threading dislocation density for a wide range of group IV p+n junctions. In the case of antiphase boundaries (APBs) of GaAs on Ge substrates, only a moderate electrical activity has been derived from these studies. On the other hand, a clear band of deep states has been demonstrated for TDs in InGaAs layers on GaAs substrates.

Surface leakage current contribution to the dynamic resistance and 1/ f noise in mid-wave mercury cadmium telluride infrared photodiodes

Surface leakage current contribution to the dynamic resistance and 1/ f noise in mid-wave Mercury Cadmium Telluride infrared photodiodes has been investigated by using gate controlled diode structures. It is reported that the behavior of bias dependent dynamic resistance as a function of gate voltage and temperature dependence of zero-bias resistance-area product can be understood by invoking contribution from surface leakage currents that are ohmic in nature. Surface leakage current variations with the variation in gate voltage are also shown to be responsible for the corresponding variations in 1/ f noise.

The influence of La-substitution on the micro-structure and ferroelectric properties of chemical-solution-deposited BiFeO3 thin films

La-substituted BiFeO3 (BFO) thin films were formed by depositing sol–gel solutions on Pt/Ti/SiO2/Si (1 0 0) structures. No secondary phase was observed by La-atom-substitution up to 20% in BFO thin films. The micro-structures of the films were changed with an increase in La concentration, which influenced the ferroelectric properties of the films. The dielectric constant of a BFO film was approximately 90 at 1 MHz and it increased to 125 in a 20% La-substituted BFO film, which was probably due to the size effect of grains. The substitution of La atoms in BFO films reduced the leakage current as well as remanent polarization. The leakage current contribution in the hysteresis loop was negligible when the loops were measured at above 20 kHz. The obtained saturated remanent polarization was 50 µC cm−2 in a 5% La-substituted BFO film at 100 kHz.

Thermally stimulated current method applied on diodes with high concentration of deep trapping levels

We propose an improved method of thermally stimulated currents (TSC) spectra analysis in the case of diodes having a concentration of traps higher than that of doping impurities. Beside the calculation of trap concentrations from TSC peaks analysis, the method allows us to evaluate the density and the type of the very deep trapping level which, due to the contribution of leakage current, can not be detected in a real TSC experiment. The proposed method is applied to a p+-n Silicon diode irradiated with 1.82×1013neutrons/cm2.

Charge trapping in very thin high-permittivity gate dielectric layers

The trapping of charge carriers in very thin SiOx/ZrO2 and SiOx/TiO2 gate dielectric stacks during constant gate voltage stress of metal–oxide–semiconductor capacitors has been investigated. The increase of the gate current density observed during the gate voltage stress has been analyzed, taking into account both the buildup of charges in the layer as well as the stress-induced leakage current contribution. From data analysis, the cross section of traps generated during the electrical stress is estimated. It is suggested that these traps are probably ZrOH and TiOH neutral centers that are related to the breaking of bridging O bonds by mobile H+ protons followed by the trapping of these protons at ZrO or TiO sites.

Fatigue, rejuvenation and self-restoring in ferroelectric thin films

Abstract The switching, fatigue and rejuvenation phenomena of ferroelectric PZT thin films with differently processed electrode-PZT interfaces and of different thicknesses have been investigated. The ferroelectric contribution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several salient features of the above phenomena. Incorporating our present results with already established properties of PZT thin films, a set of characteristic features of switching, fatigue and rejuvenation is formulated. This set is interpreted using a framework which takes into account the ferroelectric and semiconductor properties of the system. The key issues of the framework are: (i) Strong inhomogeneous built-in electric field exists in virgin films due to contact phenomena. (ii) Extra near-electrode space-charge layers are created during polarization reversal and destroyed by d.c. rejuvenating fields or by the field of fatiguing pulses. (iii) The built-in electric field is affected by these space-charge layers and then, in its turn, governs the evolution of the switching parameters (remanent-polarization, coercive field) of the film during fatigue and rejuvenation. (iv) Near-electrode nucleation of opposite domains is believed to create the extra near-electrode space-charge layers. Therefore, this nucleation seems to be responsible for the fatigue and for the sensitivity of fatigue to the surfacial properties of the film. This approach explains the thickness dependence of the coercive field, the variation of remanent polarization and coercive field with the number of switching cycles, and the rejuvenation phenomena including self-restoring.