Charging of radiation induced defects in RF MEMS dielectric films

The paper investigates the charging of radiation induced defects in Si₃N₄ and SiO₂ dielectric films, which are used in RF-MEMS switches. The radiation has been performed with 5MeV alpha particles. The assessment has been carried out in Metal-Insulator-Metal capacitors with the thermally stimulated depolarization currents and discharge current transient methods. This allowed monitoring the defects introduction as a function of radiation fluence. The defects electrical characteristics that are the activation energy and corresponding depolarization time constant were determined from the evolution of the thermally stimulated current spectra and the transient response of discharge currents at different temperatures.     

Investigation of charging mechanisms in metal-insulator-metal structures

In this paper we have investigated the temperature dependence of the charging effects in Metal-Insulator-Metal structures, aiming to obtain a better insight on the charging mechanism of RF-MEMS switch insulating layer. The accumulated charge kinetics have been monitored through the transient response of the depolarization current. The transient response is shown to follow rather a stretched exponential law. The time scale of the process is found to be thermally activated with activation energy determined by Arrhenius plot. The results have been compared to thermally stimulated depolarization current assessment.     

Voltage and temperature effect on dielectric charging for RF-MEMS capacitive switches reliability investigation

In this paper, we study the effect of stress voltage and temperature on the dielectric charging and discharging processes of silicon nitride thin films used in RF-MEMS capacitive switches. The investigation has been performed on PECVD-SiN_x dielectric materials deposited under different deposition conditions. The leakage current was found to obey the Poole–Frenkel law. The charging current decay was found to be affected by the presence of defects which are generated by electron injection at high electric fields. At high temperatures power law decay was monitored. Finally, the temperature dependence of leakage current revealed the presence of thermally activated mechanisms with similar activation energies in all materials.     

Alpha particle radiation effects in RF MEMS capacitive switches

The paper investigates the effect of 5 MeV alpha particle irradiation in RF MEMS capacitive switches with silicon nitride dielectric film. The investigation included MIM capacitors in order to obtain a better insight on the irradiation introduced defects in the dielectric film. The assessment employed the thermally stimulated depolarization currents method for MIM capacitors and the capacitance–voltage characteristic for MEMS switches. Asymmetric charging was monitored in MIM capacitors due different contact electrodes and injected charge interactions.     

Determination of bulk discharge current in the dielectric film of MEMS capacitive switches

The present work presents a new method to calculate the discharge current in the bulk of dielectric films of MEMS capacitive switches. This method takes into account the real MEMS switch with non uniform trapped charge and air gap distributions. The assessment of switches with silicon nitride dielectric film shows that the discharge current transient seems to obey the stretched exponential law. The decay characteristics depend on the polarization field’s polarity, a fact that comes along with experimental results obtained from the thermally stimulated depolarization currents (TSDC) method used in MIM capacitors.     

Assessment of dielectric charging in electrostatically driven MEMS devices: A comparison of available characterization techniques

The present work investigates the results of different characterization methods for the dielectric charging phenomenon applicable to metal–insulator–metal (MIM) capacitors and electrostatically actuated micro-electro-mechanical-systems (MEMS). The discharge current transients (DCT), thermally stimulated depolarization current (TSDC) and Kelvin probe force microscopy (KPFM) assessment methods have been applied to either MIM capacitors or electrostatic capacitive MEMS switches or both. For the first time, the KPFM methodology has been used to create a link between the results obtained from the DCT and TSDC techniques applicable for MIM and the results from MEMS switches. The comparison shows that the application of KPFM method to MIM and MEMS leads to the same results on the electrical properties of the dielectric material. This provides a novel powerful tool for the assessment of dielectric charging for MEMS switches using MIM capacitors which have much simpler layer structure. On the other hand the TSDC method reveals a continuous distribution of relaxation time constants, which supports the dependence of relaxation time constant calculated for MEMS on the duration of the observation time window.     

Free ion transport in the insulator layer and electron-ion exchange at an insulator-semiconductor phase boundary produced as a result of thermally stimulated ionic depolarization of silicon MOS structures

The nature of thermally stimulated depolarization currents in silicon MOS structures is investigated. The analysis is based on the experimentally established fact that the activation energy of the depolarization current in the initial section of growth is independent of the magnitude of the depolarizing voltage and on the previously discovered phenomenon of the formation of neutral associates ion + electron at the insulator-semiconductor interface. Transport of free ions in the insulator layer (the transit time is of a thermal activation character) and electron-ion exchange processes at the Si-SiO₂ phase boundary, which include tunneling ionization (decay) of neutral associates, are studied. The ion transfer in SiO₂ layers, found from the thermally stimulated depolarization curves using the developed theory, agrees well with data from independent experiments. Fiz. Tekh. Poluprovodn. 33, 962–968 (August 1999)     

Reliability assessment of SiO2/ZrO2 stack gate dielectric on strained-Si/Si0.8Ge0.2 heterolayers under dynamic and AC stress

The reliability characteristics of SiO₂/ZrO₂ gate dielectric stacks on strained-Si/Si_0.8Ge_0.2 have been investigated under dynamic and pulsed voltage stresses of different amplitude and frequency in order to analyze the transient response and the degradation of oxide as a function of stress parameters. The current transients observed in dynamic voltage stresses have been interpreted in terms of the charging/discharging of interface and bulk traps. The evolution of the current during unipolar pulsed voltage stresses shows the degradation being much faster at low frequencies than at high frequencies. Results have been compared with those obtained after CVS, as a function of injected charge and pulse frequency.     

Enhanced gate induced drain leakage current in HfO2 MOSFETs

The substrate current of high-κ dielectric MOSFETs has been studied using dc sweep and transient (down to 100 μs per I-V curve) electrical measurements. These measurements reveal trap-assisted substrate current components in addition to the traditional bell-shaped impact ionization current. By separating the transversal and lateral electric field contributions, the gate induced drain leakage (GIDL) is shown to dominate the substrate current at low gate biases. At high gate biases, tunneling of valence band electrons from the bulk to the gate dominates. The results show that the GIDL current is the result of band-to-band tunneling assisted by traps located at the HfO₂/SiO₂ interface and transition layer, and not the result of oxide charging.     

Electrical characterization and analysis techniques for the high-κ era

Various conventional and novel electrical characterization techniques have been combined with careful, robust analysis to properly evaluate high-κ gate dielectric stack structures. These measurement methodologies and analysis techniques have enhanced the ability to separate pre-existing defects that serve as fast transient charging and discharging sites from defects generated with stress. In addition, the differentiation of electrically active bulk high-κ traps, silicon substrate interface traps, and interfacial layer traps has been effectively demonstrated.     

Degradation of mercuric iodide crystals on aging

Mercuric iodide single crystals were grown and characterized by studying their spectral response of photoconductivity, thermally stimulated current, dielectric constant and di-electric loss as a function of frequency. The as-grown crystals have high resistivity, good photo-sensitivity, low dielectric constant and loss at low frequencies, etc. On aging, the crystals show degradation in their properties when they were stored in air, whereas the crystals stored in an iodine chamber do not exhibit any degradation. The degradation of the properties have been interpreted in terms of surface evaporation of HgI₂ and consequently formation of a surface layer rich in mercuric atoms. The effect of a dc bias on aged (degraded) samples shows restoration of the properties. The results could be interpreted in terms of polarization of mobile defects and formation of space charge layers which enhance a high internal field in the crystals, hence the restoration of the properties.     

A study of the gold acceptor in a silicon p+n junction and an n-type MOS capacitor by thermally stimulated current and capacitance measurements

The thermally stimulated current and capacitance responses of a gold doped p⁺n junction and n-type MOS capacitor were measured experimentally and modeled theoretically for the case of majority-carrier defect charging. The gold acceptor atoms are initially charged with electrons at low temperatures, and during the heating cycle, excess electrons are released from the gold atoms. The thermally stimulated current response for this phase is similar in both structures and has a distinctive peak-and-valley shape and an emission temperature about 220 K. During the steady-state phase, a current peak occurs in the MOS capacitance response. A physical model was developed and the influence of various parameters on the current and capacitance measurements was quantified. Various analytical schemes are described which allow rapid identification of the gold defect center and rapid computation of its density. A simple and inexpensive apparatus is described which is capable of heating rates as high as 10 K/s.     

Properties of thin oxide-nitride-oxide stacked films

Electronic conduction, charge trapping and dielectric breakdown were studied on thin stacked layers of SiO₂-Si₃N₄-SiO₂ with Al or poly-Si gate on Si. Conductivity and breakdown strength are roughly the same as observed on single SiO₂ films but the average dielectric constant is higher than that for SiO₂. Stacks with plasma CVD SiO₂ layers show somewhat poorer breakdown strengths than those with thermally grown SiO₂ films. The charging behavior of the stacks is more pronounced than that of single films. Moreover, they break down at a lower total injected charge.     

Temperature and annealing effects on InAs nanowire MOSFETs

We report on temperature dependence on the drive current as well as long-term effects of annealing in vertical InAs nanowire Field-Effect Transistors. Negatively charged traps in the HfO₂ gate dielectric are suggested as one major factor in explaining the effects observed in the transistor characteristics. An energy barrier may be correlated with an un-gated InAs nanowire region covered with HfO₂ and the effects of annealing may be explained by changed charging on defects in the oxide. Initial simulations confirm the general effects on the I-V characteristics by including fixed charge.     

Generation of minority charge carriers at the semiconductor surface during thermally activated ionic depolarization of metal-insulator-semiconductor structures

Relaxation signals represented by the temperature dependences of current J(T) and high-frequency capacitance C(T) and generated in the course of the thermally stimulated depolarization of a metal-insulator-semiconductor structure were analyzed numerically. Both the depletion of ionic traps located at the insulator-semiconductor interface and the generation of minority charge carriers from a bulk center with the activation energy _{E D} were taken into account.     

Temperature study of the dielectric polarization effects of capacitive RF MEMS switches

This paper investigates both theoretically and experimentally the dielectric charging effects of capacitive RF microelectromechanical system switches with silicon nitride as dielectric layer. Dielectric charging caused by charge injection under voltage stress was observed. The amphoteric nature of traps and its effect on the switch operation were confirmed under both positive and negative control voltages. It has been confirmed that charging is a complicated process, which can be better described through the stretched exponential relaxation. This mechanism is thermally activated with an activation energy being calculated from the temperature dependence of the capacitance transient response. The charging mechanism, which is responsible for the pull-out voltage and the device failure, is also responsible for the temperature-induced shift of the capacitance minimum bias.     

Experimental observations of temperature-dependent flat band voltage transients on high-k dielectrics

In this work, we show the existence of flat band voltage transients in ultrathin Gd₂O₃ dielectric films on silicon, one of the high-k dielectrics nowadays proposed to substitute silicon oxide as the dielectric gate on the future complementary metal-oxide-semiconductor circuit generations. These transients were obtained by recording the gate voltage while keeping the capacitance constant at the value measured at initial flat band condition. The dependencies of transient time constant and amplitude on dielectric thickness and temperature suggest that there are tunnelling assisted processes involved. Time constant appears to be independent on the temperature, whereas the amplitude of the transients is thermally activated with energies in the range of soft-optical phonons usually reported for high-k dielectrics. In the case of gadolinium oxide a phonon energy of 55 ± 10 meV has been obtained. Leakage current behaviour at high electric fields confirms that conduction is governed by a phonon-assisted tunnelling mechanism between localized states in the band gap of the insulator.     

Uniformity of deep levels in semi-insulating InP obtained by multiple-step wafer annealing

The uniformity of deep levels in semi-insulating InP wafers, which have been obtained by multiple-step wafer annealing under phosphorus vapor pressure, was studied using the thermally stimulated current (TSC) and photoluminescence (PL) methods. Only three traps related to Fe, T₀ (ionization energy E_i=0.19 eV), T₁ (0.25 eV), and T₂ (0.33 eV), probably forming complex defects, were observed in the wafer and they exhibited a relatively uniform distribution. PL spectra relating to phosphorus vacancies observed in some regions of the wafer are correlated with a small TSC signal having an ionization energy of 0.43 eV.     

Transient Negative Capacitance Effect in Atomic‐Layer‐Deposited Al2O3/Hf0.3Zr0.7O2 Bilayer Thin Film

The negative capacitance (NC) effect is now attracting a great deal of attention in work towards low‐power operation of field effect transistors and extremely large capacitance density in dynamic random access memory. However, to date, observation of the NC effect in dielectric/ferroelectric bilayer capacitors has been limited to the use of epitaxial ferroelectric thin films based on perovskite crystal structures, such as Pb(Zr,Ti)O₃ and BaTiO₃, which is not compatible with current complementary metal oxide semiconductor technology. This work, therefore, reports on the transient NC effect in amorphous‐Al₂O₃/polycrystalline‐Hf_0.3Zr_0.7O₂ bilayer systems prepared using atomic layer deposition. The thin film processing conditions are carefully tuned to achieve the appropriate ferroelectric performances that are a prerequisite for the examination of the transient NC effect. Capacitance enhancement is observed in a wide voltage range in 5–10 nm thick Al₂O₃/Hf_0.3Zr_0.7O₂ bilayer thin films. It is found that the capacitance of the dielectric layer plays a critical role in the determination of additional charge density induced by the NC effect. In addition, inhibition of the leakage current is important for stabilization of nonhysteretic charge–discharge behavior of the bilayers. The mean‐field approximation combined with classical Landau formalism precisely reproduces the experimental results.     

Establishment of specific features of electron localization at <Emphasis Type="Italic">U</Emphasis><Superscript>−</Superscript> centers in semiconductors from thermally stimulated currents

The specific features of thermally stimulated currents in semiconductors containing U ^? centers are treated theoretically in comparison with the corresponding features for semiconductors containing defects with a positive correlation energy or single-level centers. It is shown that the analysis of the curves of thermally stimulated currents normalized to the maximum current in respect to the shape and to the presence or absence of a shift of the temperature maximum of the curve in relation to the initial occupancy provides an extra necessary criterion for identifying defects with different parameters of binding of electrons. The results can be used in analyzing experimental data on thermally stimulated currents that exhibit features inexplicable in the context of the often used model of single-level centers.