微晶硅薄膜晶体管稳定性研究

对有源区处于结构过渡区的微晶硅底栅薄膜晶体管，测试其偏压衰退特性时，观察到一种“自恢复”的衰退现象.当栅和源漏同时施加10 V的偏压时，测试其源-漏电流随时间的变化，发现源-漏电流先衰减、而后又开始恢复上升的反常现象.而当采用栅压为10 V、源-漏之间施加零偏压的模式时，源-漏电流随时间呈先是几乎指数式下降、随之是衰退速度减缓的正常衰退趋势.就此现象进行了初步探讨. 关键词： 过渡区硅材料 微晶硅薄膜晶体管 稳定性 自恢复衰退     

High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current I_Dsat, maximal transconductance g_m, and the positive shift of threshold voltage V_TH at high drain-source voltage V_DS. The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with V_DS=20 V and V_GS=0 V applied to the device for 10⁴ sec, the SiN passivation decreases the stress-induced degradation of I_Dsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of I_Dsat, which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted.     

Hot-carrier degradation for 90nm gate length LDD-NMOSFET with ultra-thin gate oxide under low gate voltage stress

The hot-carrier degradation for 90~nm gate length lightly-doped drain (LDD) NMOSFET with ultra-thin (1.4~nm) gate oxide under the low gate voltage (LGV) (at V_g=V_th, where V_th is the threshold voltage) stress has been investigated. It is found that the drain current decreases and the threshold voltage increases after the LGV (V_g=V_th stress. The results are opposite to the degradation phenomena of conventional NMOSFET for the case of this stress. By analysing the gate-induced drain leakage (GIDL) current before and after stresses, it is confirmed that under the LGV stress in ultra-short gate LDD-NMOSFET with ultra-thin gate oxide, the hot holes are trapped at interface in the LDD region and cannot shorten the channel to mask the influence of interface states as those in conventional NMOSFET do, which leads to the different degradation phenomena from those of the conventional NMOS devices. This paper also discusses the degradation in the 90~nm gate length LDD-NMOSFET with 1.4~nm gate oxide under the LGV stress at V_g=V_th with various drain biases. Experimental results show that the degradation slopes (n) range from 0.21 to 0.41. The value of n is less than that of conventional MOSFET (0.5-0.6) and also that of the long gate length LDD MOSFET (\sim0.8).     

The fabrication and characterization of 4H SiC power UMOSFETs

The fabrication of 4H-SiC vertical trench-gate metal-oxide-semiconductor field-effect transistors(UMOSFETs) is reported in this paper.The device has a 15-μm thick drift layer with 3×1015 cm-3 N-type doping concentration and a 3.1μm channel length.The measured on-state source-drain current density is 65.4 A/cm2 at Vg = 40 V and VDS = 15 V.The measured threshold voltage(Vth) is 5.5 V by linear extrapolation from the transfer characteristics.A specific on-resistance(Rsp-on) is 181 mΩ·cm2 at Vg = 40 V and a blocking voltage(BV) is 880 V(IDS = 100 μA@880V) at Vg = 0 V.     

Actions of negative bias temperature instability (NBTI) and hot carriers in ultra-deep submicron p-channel metal——oxide——semiconductor field-effect transistors (PMOSFETs)

Hot carrier injection (HCI) at high temperatures and different values of gate bias V_g has been performed in order to study the actions of negative bias temperature instability (NBTI) and hot carriers. Hot-carrier-stress-induced damage at V_g=V_d, where V_d is the voltage of the transistor drain, increases as temperature rises, contrary to conventional hot carrier behaviour, which is identified as being related to the NBTI. A comparison between the actions of NBTI and hot carriers at low and high gate voltages shows that the damage behaviours are quite different: the low gate voltage stress results in an increase in transconductance, while the NBTI-dominated high gate voltage and high temperature stress causes a decrease in transconductance. It is concluded that this can be a major source of hot carrier damage at elevated temperatures and high gate voltage stressing of p-channel metal--oxide--semiconductor field-effect transistors (PMOSFETs). We demonstrate a novel mode of NBTI-enhanced hot carrier degradation in PMOSFETs. A novel method to decouple the actions of NBTI from that of hot carriers is also presented.     

高场应力及栅应力下AlGaN/GaN HEMT器件退化研究

采用不同的高场应力和栅应力对AlGaN/GaN HEMT器件进行直流应力测试,实验发现：应力后器件主要参数如饱和漏电流,跨导峰值和阈值电压等均发生了明显退化,而且这些退化还是可以完全恢复的;高场应力下,器件特性的退化随高场应力偏置电压的增加和应力时间的累积而增大;对于不同的栅应力,相对来说,脉冲栅应力和开态栅应力下器件特性的退化比关态栅应力下的退化大.对不同应力前后器件饱和漏电流,跨导峰值和阈值电压的分析表明,AlGaN势垒层陷阱俘获沟道热电子以及栅极电子在栅漏间电场的作用下填充虚栅中的表面态是这些不同应 关键词： AlGaN/GaN HEMT器件 表面态(虚栅) 势垒层陷阱 应力     

The switch of the worst case on NBTI and hot-carrier reliability for 0.13 μm pMOSFETs

This investigation describes experiments on two sizes of p-channel metal-oxide-semiconductor field-effect-transistors (pMOSFETs), to study the negative bias temperature instability (NBTI) and hot-carrier (HC) induced degradation. This work demonstrates that the worst condition for pMOSFETs under HC tests occurs in CHC (channel HC, stressed at V_g = V_d) mode at high temperature. This study also shows that the worst degradation of pMOSFETs should occur in NBTI. This inference is based on a comparison of results for forward saturation current (I_ds,f) and reverse saturation current (I_ds,r) obtained in NBTI and HC tests.     

Electron-nuclear-double-resonance of the VAl center in MgO

An ENDOR study of a hole center in MgO with g_|=2.0032±0.0001 and g_⊥=2.0385±0.0001 reveals that the hole interacts with an axial aluminum ion with A_⊥=±0.178±0.008 MHz, A_⊥=±0.074±0.008 MHz, and P= ±0.366±0.002 MHz. The structure of the center is consistent with the label, V_Al. It is suggested that the V_Al center may have been mistaken in the past for the V^- center because of the similarity of their g-values, method of production, and thermal properties.     

Kink effect in AlGaN/GaN high electron mobility transistors by electrical stress

The kink effect is studied in an AlGaN/GaN high electron mobility transistor by measuring DC performance during fresh, short-term stress and recovery cycle with negligible degradation. Vdg plays an assistant role in detrapping electrons and short-term stress results in no creation of new category traps but an increase in number of active traps. A possible mechanism is proposed that electrical stress supplies traps with the electric field for activation and when device is under test field-assisted hot-electrons result in electrons detrapping from traps, thus deteriorating the kink effect. In addition, experiments show that the impact ionization is at a relatively low level, which is not the dominant mechanism compared with trapping effect. We analyse the complicated link between the kink effect and stress bias through groups of electrical stress states: Vds = 0-state, off-state, on-state (on-state with low voltage, high-power state, high field state). Finlly, a conclusion is drawn that electric field brings about more severe kink effect than hot electrons. With the assistance of electric field, hot electrons tend to be possible to modulate the charges in deep-level trap.     

High-Frequency ESR Measurements of <Emphasis Type="Italic">S</Emphasis> = 1/2 1-D Heisenberg Antiferromagnetic Zig-Zag Chain (VO)(SO<Subscript>4</Subscript>)(2,2-bpy)

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO₄)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V⁴⁺ ion and g _|| = 1.925 ± 0.001 and g _⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO₄)(2,2-bpy).     

Use of an electrical aerosol detector (EAD) for nanoparticle size distribution measurement

Recently, Nanoparticle Surface Area Monitor (NSAM, TSI model 3550) and EAD (EAD, TSI Model 3070A) have been commercially available to measure the integral parameters (i.e., total particle surface area and total particle length) of nanoparticles. By comparison, the configuration of the EAD or NSAM is similar to that of electrical mobility analyzer of the early generation for particle size distribution measurement. It is therefore possible to use the EAD or NSAM as a particle sizer. To realize the objective of using the EAD as a sizer, we characterized the average electrical charges of monodisperse particles passing through the EAD particle charger and ion trap set at voltages ranging from 20 to 2500 V. The average charge data collected at different ion-trap voltages were then summarized by the empirical correlation using the parameter of Z _p *V, where Z _p is the particle electrical mobility and V is the ion-trap voltage. A data-reduction scheme was further proposed to retrieve the size distribution of sampled particles from the EAD readout at different ion-trap voltages. In the scheme, the functional format of each mode in a number size distribution of particles was assumed as log-normal, but the number of modes in an entire size distribution is not limited. A criterion was used to best fit the simulated EAD readouts with experimental ones by varying the count median diameter (CMD), geometric standard deviation (σ _g), and total particle number (N _t ) of each mode in a particle size distribution. Experiments were performed to verify the proposed scheme.     

Intermittent discharging of nickel–metal hydride secondary battery

A nickel–metal hydride secondary battery is discharged intermittently through a switch of 30 s on/30 s off mode via an external load R _r. The discharge current i _g is measured during switch-on and an open-circuit voltage V _oc during switch-off. In the course of discharge run, i _g drops at some time by depletion of an active material within the positive electrode. The pulse shapes of i _g and V _oc in each on/off duration are featureless before the i _g drop, satisfying the relation V _oc=i _g(R _i+R _r) (R _i being the internal resistance of a battery). After the i _g drop, they become time dependent; yet, the above relation still holds. It is found that V _oc changes continuously through the onset times of switch-on and -off.     

Highly stable amorphous indium‐zinc‐oxide thin‐film transistors with back‐channel wet‐etch process

The stabilities of amorphous indium‐zinc‐oxide (IZO) thin film transistors (TFTs) with back‐channel‐etch (BCE) structure are investigated. A molybdenum (Mo) source/drain electrode was deposited on an IZO layer and patterned by hydrogen peroxide (H₂O₂)‐based etchants. Then, after etching the Mo layer, SF₆ plasma with direct plasma mode was employed and optimized to improve the bias stress stability. Scanning electron microscopy and X‐ray photoelectron spectroscopic analysis revealed that the etching residues were removed efficiently by the plasma treatment. The modified BCE‐ TFTs showed only threshold voltage shifts of 0.25 V and –0.20 V under positive/negative bias thermal stress (P/NBTS, V_GS = ±30 V, V_DS = 0 V and T = 60 °C) after 12 hours, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of self-implanted silicon annealed under enhanced hydrostatic pressure

Implantation of any ions at a sufficiently high dose and energy (E) into single-crystalline Si leads to the creation of amorphous Si (aSi), with damages peaking near the projected range (R _p) of implanted species. Enhanced hydrostatic pressure (HP) at a high temperature (HT) influences the recrystallization of aSi. The structure of self-implanted Czochralski silicon (Si⁺ dose, D=2×10¹⁶ cm^?2, E=150 keV, R _p=0.22 μm) processed for 5 h at 1400 or 1520 K under HPs up to 1.45 GPa was investigated by X-ray, secondary ion mass spectrometry and photoluminescence methods. The implantation of Si produces vacancies (V) and self-interstitials (Si_i). Vacancies and Si_is form complex defects at HT–HP, also with contaminants (e.g. oxygen, always present in Czochralski silicon). The mobility and recombination of V and Si_i as well as the kinetics of recrystallization are affected by HP, thus processing at HT–HP affects the recovery of aSi.     

The reliability of AlGaN/GaN high electron mobility transistors under step-electrical stresses

In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors (HEMTs) still lack solid reliability. Devices under accelerated DC stress tests (off-state, V_DS =0 state, and on-state step-stress) are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] (Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415). However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.     

Deposition pressure effect on the surface roughness scaling of microcrystalline silicon films

The scaling behaviour of surface roughness evolution of microcrystalline silicon (μc-Si:H) films prepared by very-high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) has been investigated by using a spectroscopic ellipsometry (SE) technique. The growth exponent β was analysed for the films deposited under different pressures P_g. The results suggest that films deposited at P_g = 70 Pa have a growth exponent β about 0.22, which corresponds to the definite diffusion growth. However, abnormal scaling behaviour occurs in the films deposited at P_g = 300 Pa. The exponent β is about 0.81 that is much larger than 0.5 of zero diffusion limit in the scaling theory. The growth mode of μ c-Si:H deposited at P_g= 300 Pa is clearly different from that of μc-Si:H at P_g = 70 Pa. Monte Carlo simulations indicate that the sticking process and the surface diffusion of the radicals are two key factors to affect the growth mode under different pressures. Under P_g= 300 Pa, β>0.5 is correlated with the strong shadowing effect resulting from the larger sticking coefficient.     

Oxygen hole centers in coesite,a high pressure phase of SiO2

Electron spin resonance (ESR) spectra have been measured for coesite synthesized under high pressure condition from natural quartz and irradiated by γ-rays at 77K. The prominent signals detected at 77 K have an anisotropicg-factor of orthorhombic symmetry,g ₁=2.0015,g ₂=2.0055 andg ₃=2.065 and are ascribed to an oxygen related hole center in coesite. The observed signal atg _‖=2.0033 andg _⊥=2.0085 might be related with an O- or O₂-type hole center.     

SiGe电荷注入晶体管的直流特性模型

为了能直观地体现SiGe/Si电荷注入晶体管的收集极电流与漏源电压的关系，利用输入端SiGe/Si量子阱中二维空穴气的隧道模型，建立起此类器件的输入输出数学模型，并利用MATLAB软件对所建模型进行了模拟，结果显示在漏源电压约为1.5 V时，漏电流出现较强的负微分电阻效应，与文献报道结果符合. 关键词： SiGe/Si异质结 电荷注入晶体管 二维空穴气 隧道效应     

Effects of DC and AC stress on the VT shift of AlGaN/GaN MIS-HEMTs

AlGaN/GaN MIS-HEMTs with adjusted V_T were fabricated using a recess gate to investigate the effect on actual operation when the polarity of the gate voltage is opposite in the on- and off-state. The direction and time exponents of V_T shift depend on the polarity of the gate bias stress. Electrons detrapping from the Al₂O₃/AlGaN interface trap site to AlGaN under negative gate bias stress has to overcome the energy barrier, resulting in a higher temperature dependence. In addition, the unaffected g_m and SS show that the degradation occurred primarily at the Al₂O₃/AlGaN interface rather than channel or mobility degradation. For unipolar and bipolar AC stresses, the time exponent of the V_T shift during stress time has two values, and a relatively low value during relaxation after bipolar AC stress. These results may be due to the further degradation by V_min at the broader energy levels of the Al₂O₃/AlGaN interface.