A reliable approach to charge-pumping measurements in MOS transistors

A new and accurate approach to charge-pumping measurements for the determination of the Si-SiO2interface state density directly on MOS transistors is presented. By a careful analysis of the different processes of emission of electrons towards the conduction band and of holes towards the valence band, depending on the charge state of the interface, all the previously ill-understood phenomena can be explained and the deviations from the simple charge-pumping theory can be accounted for. The presence of a geometric component in some transistor configurations is illustrated and the influence of trapping time constants is discussed. Furthermore, based on this insight, a new technique is developed for the determination of the energy distribution of interface states in small-area transistors, without requiring the knowledge of the surface potential dependence on gate voltage.     

Charge pumping in MOS devices

Gate pulses applied to MOS transistors were found to stimulate a net flow of charge into the substrate. Investigation of this effect revealed a charge-pumping phenomeonon in MOS gate-controlled-diode structures. A first-order theory is given, whereby the injected charge is separated into two components. One component involves coupling via fast surface states at the Si-SiO2interface under the gate, while the other involves recombination of free inversion-layer charge into the substrate.     

Charge-pumping characterization of SiO2/Si interface invirgin and irradiated power VDMOSFETs

The applicability of charge-pumping technique to characterize the oxide/silicon interface in standard power Vertical Double-diffused (VD)MOS transistors is studied. Qualitative analysis of the charge-pumping threshold and flat-band voltage distributions in the VDMOS structure, supported with rigorous transient numerical modeling of the charge-pumping effect, shows that the measurements can be carried out in the subthreshold region. This conclusion is confirmed by various experimental results. The characteristics, i.e. charge-pumping current versus gate top level, is studied in detail. The changes in the characteristics after γ-ray irradiation are analyzed. A charge-pumping-based method for separate extraction of interface state density and density of charge trapped in the oxide after irradiation of VDMOSFETs is proposed. The validity and limitations of the method are studied by experiments and modeling     

Hot-carrier effects on interface-trap capture cross sections inMOSFETs as studied by charge pumping

A rapid charge-pumping method was used to measure the interface-trap parameters in MOSFETs. The geometric mean of the electron and hole interface-trap capture cross sections decreases significantly (as much as two orders of magnitude) after Fowler-Nordheim (F-N) injection, and gradually recovers toward its original value. This effect is consistent with the interface-trap transformation process observed in MOS capacitors     

The charge-pumping technique for grain boundary trap evaluation inpolysilicon TFTs

Polysilicon thin-film transistor (poly-Si TFT) characteristics were evaluated by using the charge-pumping technique. The recombination current at the grain boundary traps is measured as the charge-pumping current in this technique. Therefore, the influence of the grain boundary traps is directly evaluated. It was confirmed that a large number of acceptorlike and donorlike traps exist at the grain boundaries in poly-Si TFTs. The trap density is derived from the pulse falltime dependence of the charge-pumping current. The influence of process temperature on trap properties is examined using the charge-pumping technique     

A novel method for extracting the metallurgical channel length ofMOSFETs using a single device

A new charge-pumping method with dc source/drain biases and specified gate waveforms is proposed to extract the metallurgical channel length of MOSFETs by using a single device. Using two charge-pumping currents of a single nMOSFET measured under different V _GL (V_GH for pMOSFETs), the metallurgical channel length can be easily extracted with an accuracy of 0.02 μm. It is shown that the proposed novel method is self-consistent with the results obtained by the charge-pumping current measured from multidevices under different gate pulse waveforms and bias conditions     

A new technique for measuring lateral distribution of oxide chargeand interface traps near MOSFET junctions

A technique to measure the lateral distribution of both interface traps and trapped oxide charge near the source-drain junctions in MOSFETs is presented. Its basic principle is described. This technique derives from the charge-pumping method, is easy to implement, and allows ready separation of the interface-trap and oxide charge components. Examples are shown for hot-carrier stressed MOS transistors     

Double-pulse charge pumping in MOSFETs

A double-pulse charge-pumping (DPCP) method is described. The method enables measuring of an energy distribution of interface states in both the lower and upper halves of bandgap and allows determination of capture cross section energy distribution for electrons in the upper half of the bandgap in n-channel MOSFETs and for holes in the lower half in p-channel MOSFETs. The method supplements the CP method's family. Its major advantage consists in enhanced immunity against the parasitic geometrical components of the CP current     

Profiling of Nitride-Trap-Energy Distribution in SONOS Flash Memory by Using a Variable-Amplitude Low-Frequency Charge-Pumping Technique

A variable-amplitude low-frequency charge-pumping technique is proposed to characterize the nitride-trap energy and spatial distributions in SONOS Flash memory cells. A numerical model based on Shockley-Read-Hall-like electron tunneling capture is used to correlate a charge-pumping current with the nitride-trap energy and position. By changing the frequency and pulse amplitude in charge-pumping measurement, a nitride-trap density, as a function of the trap position and energy, can be extracted.     

System level simulation of a micro resonant accelerometer with geometric nonlinear beams

Geometric nonlinear behaviors of micro resonators have attracted extensive attention of MEMS (microelectro-mechanical systems) researchers, and MEMS transducers utilizing these behaviors have been widely researched and used due to the advantages of essentially digital output.Currently, the design of transducers with nonlinear behaviors is mainly performed by numerical method and rarely by system level design method.In this paper, the geometric nonlinear beam structure was modeled and established as a reusable library component by system level modeling and simulation method MuPEN (multi port element network).A resonant accelerometer was constructed and simulated using this model together with MuPEN reusable library.The AC (alternating current) analysis results of MuPEN model agreed well with the results of architect model and the experiment results shown in the existing reference.Therefore, we are convinced that the beam component based on MuPEN method is valid, and MEMS system level design method and related libraries can effectively model and simulate transducers with geometric nonlinear behaviors if appropriate system level components are available.     

Two-layered image compression using 2G bandelets and wavelets

An image can be decomposed into the structural component and the geometric textural component.Based on this idea,an efficient two-layered compressing algorithm is proposed,which uses 2nd generation bandelets and wavelets.First,an original image is decomposed into the structural component and the textural component,and then these two components are compressed using wavelets and 2nd generation bandelets respectively.Numerical tests show that the proposed method works better than the bandelets and JPEG2000 in some specific SAR scene.     

Lateral Nonuniformity Effects of Border Traps on the Characteristics of Metal–Oxide–Semiconductor Field-Effect Transistors Subjected to High-Field Stresses

The lateral nonuniformity (LNU) effects of border traps are studied by exploring both the high- and low-frequency characteristics in N-type channel metal-oxide-semiconductor field-effect transistors. According to experimental data, the deterioration of nonuniformity is significantly enhanced at low frequencies. The cause may be due to the additional trapped charges of border traps (near-interface oxide traps) under the low-frequency measurement. This model is successfully simulated by the combination of low-frequency C-V curves with the heavily and lightly damaged regions. Additionally, the double-peak charge-pumping current is observed in low-frequency measurements, which can further support our hypothesis that border-trap-enhanced LNU exists. Finally, the geometric effect of the polygate and the thickness effect of the gate oxide are also investigated for the nonuniformity issue.     

基于多尺度几何分析的医学图像融合

针对医学图像,提出了一种基于多尺度几何分析的医学图像融合算法。首先,利用Contoutlet变换对待融合两幅图像进行分解,将得到的低频分量分别利用Shearlet变换分解,并采用区域能量加权平均的规则,进行一次融合得到融合低频分量;对得到的高频分量分别用小波变换进行分解,再用低频、高频取大的规则进行一次融合得到融合高频分量,最后对得到的融合高低频分量进行Contourlet逆变换得到融合结果。实验结果表明,该算法在信息熵和平均梯度等参数上有明显提升,且能更好地表征图像中不同的奇异性。     

A general model for interface-trap charge-pumping effects in MOS devices

Interface-trap charge-pumping effect is analysed on the basis of Shockley-Read-Hall theory of trapping, and a model describing the effect for any trapezoidal gate waveform and any reverse biasing source voltage is derived. A simplified version of the model which is valid for identical rise and fall times is also presented and experimentally verified. Experimental results indicate that the spatial variation of surface potential and the modulation of effective gate area by source voltage may strongly influence the charge-pumping current. It is also shown that the effect of gate-area modulation can be characterized directly from charge-pumping measurements.     

The use of charge pumping to characterize generation by interface traps

A small rectangular pulse technique for measuring charge-pumping current has been proposed as a method to characterize interface traps near midgap. It is shown theoretically and experimentally that the small rectangular pulse technique can be used to predict the surface generation current measured on a MOSFET or a gated diode. This new technique has the advantage that the measured current is at least 10 to 100 times larger than the surface generation current.     

Distribution and generation of traps in SiO2/Al2O3 gate stacks

In this work we combine charge-pumping measurements with positive constant voltage stress to investigate trap generation in SiO₂/Al₂O₃ n-MOSFET. Trap density has been scanned either in energy or in position based on charge-pumping (CP) measurements performed under different operating conditions in terms of amplitude and frequency of the gate pulse. Our results have revealed that the traps are meanly localized shallow in energy level, deeper in spatial position and they are mostly generated near the Si/SiO₂ interface.     

Minimized constrains for lateral profiling of hot-carrier-induced oxide charge and interface traps in MOSFETs

For better understanding the hot-carrier-induced reliability problems, a charge-pumping technique has been developed to profile the Q/sub ot/ and N/sub it/ directly from the experimental results. However, the key neutralization condition is acquired by trial and error, which takes much time and effort. Therefore, a technique of two-step neutralization is proposed to find out the appropriate neutralization condition in this work. This two-step neutralization combined with the error-reduction method is shown to carry out the profiling more quickly and precisely.     

Evidence of acceptor-like oxide defects created by hot-carrierinjection in n-MOSFET's: a charge-pumping study

Charge-pumping measurements and simulation of charge-pumping characteristics demonstrate that acceptor-like oxide traps (i.e. negatively charged when occupied by an electron and neutral when occupied by a hole) are created in the gate-drain overlap region of an n-MOSFET subjected to hot-electron and/or hot-hole injections (HEI and/or HHI). These traps are located in the gate-drain overlap region, and it is emphasized that the charge-pumping technique is able to detect them in addition to the damages in the channel     

Principles of transient charge pumping on partially depleted SOIMOSFETs

A new method to determine the interface trap density in partially depleted silicon-on-insulator (SOI) floating body MOSFETs is proposed for the first time. It can be considered as a "transient" charge-pumping (CP) technique in contrast to the normally used "steady-state" method. In our technique, majority carriers are removed from the floating body by applying a burst of pulses to the transistor gate. The change in the linear drain current after each pulse is used to determine the device interface trap density. The unique advantage of this method is the possibility to use it to characterize SOI MOSFETs without a body contact. The technique proposed is simple, reliable, and can be used for the characterization of deep submicron devices     

Physical Mechanism and Gate Insulator Material Dependence of Generation and Recovery of Negative-Bias Temperature Instability in p-MOSFETs

Impact of gate dielectric processing [plasma and thermal nitridation, nitrogen total dose, effective oxide thickness (EOT)] on negative-bias temperature instability (NBTI) degradation and recovery is studied. The magnitude, field, and temperature dependence of NBTI is measured using no-delay I_DLIN method and carefully compared to charge-pumping measurements. Plasma (thin and thick EOT) and thermal (thin EOT) oxynitrides show very similar temperature and time dependence of NBTI generation, which is identical to control oxides and is shown to be due to generation of interface traps. NBTI enhancement for oxynitride films is shown to be dependent on nitrogen concentration at the Si-SiO₂ interface and plasma oxynitrides show lower NBTI compared to their thermal counterparts for same total nitrogen dose and EOT. Both fast and slow NBTI recovery components are shown to be due to recovery of generated interface traps. Recovery fraction reduces at lower EOT, while for similar EOT oxynitrides show lower recovery with-respect-to control oxides. NBTI generation and recovery is explained with the framework of reaction-diffusion model.