Rm HfO Research Articles

Optimum High-k Oxide for the Best Performance of Ultra-Scaled Double-Gate MOSFETs

A widely used technique to mitigate the gate leakage in the ultra-scaled metal oxide semiconductor field effect transistors (MOSFETs) is the use of high-k dielectrics, which provide the same equivalent oxide thickness (EOT) as $\rm SiO_2$, but thicker physical layers. However, using a thicker physical dielectric for the same EOT has a negative effect on the device performance due to the degradation of 2D electrostatics. In this letter, the effects of high-k oxides on double-gate (DG) MOSFET with the gate length under 20 nm are studied. We find that there is an optimum physical oxide thickness ($\rm T_{OX}$) for each gate stack, including $\rm SiO_2$ interface layer and one high-k material. For the same EOT, $\rm Al_2O_3$ (k=9) over 3 $\rm\AA$ $\rm SiO_2$ provides the best performance, while for $\rm HfO_2$ (k=20) and $\rm La_2O_3$ (k=30), $\rm SiO_2$ thicknesses should be 5 $\rm\AA$ and 7 $\rm\AA$, respectively. The effects of using high-k oxides and gate stacks on the performance of ultra-scaled MOSFETs are analyzed. While thin oxide thickness increases the gate leakage, the thick oxide layer reduces the gate control on the channel. Therefore, the physical thicknesses of gate stack should be optimized to achieve the best performance.

Effects of RESET Current Overshoot and Resistance State on Reliability of RRAM

Current overshoot has severe effects on the reliability of resistive random access memory (RRAM). It is well known that the current overshoot during the SET process is caused by parasitic capacitance. In this letter, we observed a different type of current overshoot during the RESET process. The RESET current overshoot was confirmed to have severe effects on the endurance of RRAM. We also demonstrated the relation between the current overshoot and the intrinsic capacitive elements of each state of RRAM. Finally, an optimized pulse shape was proposed to minimize the current overshoot and was experimentally verified to significantly improve the variability and endurance in a typical RRAM device with a W/Zr/ ${\rm HfO}_{2}$ /TiN structure.

A Simulation Study of Oxygen Vacancy-Induced Variability in ${\rm HfO}_{2}$ /Metal Gated SOI FinFET

Deposition of a metal gate on high-K dielectric HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is known to generate oxygen vacancy (OVs) defects. Positively charged OVs in the dielectric affect the gate electrostatics and modulate the effective gate workfunction (WF). Count and spatial allocation of OVs varies from device-to-device and induces significant local variability in WF and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> . This paper presents the statistical models to simulate OV concentration and placement depending on the gate formation conditions. OV-induced variability is studied for SOI FinFET, and compared against the other sources of variability across the technologies. The implications of gate first and gate last processes to the OV concentration/distribution are studied. Simulations show that with channel length and gate dielectric thickness scaling, the OV-induced variability becomes a significant concern.

Excellent Current Drivability and Environmental Stability in Room-Temperature-Fabricated Pentacene-Based Organic Field-Effect Transistors With ${\rm HfO}_{2}$ Gate Insulators

Low-voltage-operating pentacene-based organic field-effect transistors (OFETs) with HfO2 gate insulators have been fabricated at room temperature. Despite its thin capacitance equivalent thickness of 3.6 nm, the room-temperature-processed HfO2 gate insulator shows a low leakage current density of 1.2×10-7 A/cm2 at a gate voltage of -2 V. Pentacene films grown on the HfO2 gate insulators have a large grain size and a highly ordered molecular structure due to the appropriate surface properties of the HfO2 gate insulators. The as-fabricated pentacene-based OFET (W/L=1300 μm/100 μm) with a HfO2 gate insulator has a low subthreshold swing of 0.13 V/decade, a large ON/OFF current ratio of 9.8×104, and a high hole mobility of 0.34 cm2V-1s-1 at an operating voltage of -2 V. Furthermore, the environmental stability in the room-temperature-fabricated pentacene-based OFETs with HfO2 gate insulators was investigated.

The Impact of X-Ray and Proton Irradiation on ${\rm HfO}_2/{\rm Hf}$-Based Bipolar Resistive Memories

This paper investigates total-ionizing dose effects on the electrical characteristics of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Hf-based bipolar resistive-random-access-memory (RRAM) devices. 10-keV x-ray irradiation does not cause significant changes in resistance at levels up to 7 Mrad( SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). Excess carriers generated by x-ray irradiation in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer recombine or are trapped at defect sites in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer or at interfaces between layers. They have no effect, however, on the conductive path of the RRAM devices. 1.8 MeV proton irradiation causes resistance degradation through simultaneous introduction of oxygen vacancies and displacement damage. TRIM simulations are used to explain the physical mechanisms of the radiation-induced damage. The devices are promising for radiation-hardened memory applications.

From MFM Capacitors Toward Ferroelectric Transistors: Endurance and Disturb Characteristics of ${\rm HfO}_{2}$-Based FeFET Devices

Ferroelectric Si:HfO2 has been investigated starting from metal-ferroelectric-metal (MFM) capacitors over metal-ferroelectric-insulator-semiconductor (MFIS) and finally ferroelectric field-effect-transistor (FeFET) devices. Endurance characteristics and field cycling effects recognized for the material itself are shown to also translate to highly scaled 30-nm FeFET devices. Positive-up negative-down as well as pulsed Id-Vg measurements illustrate how ferroelectric material characteristics of MFM capacitors can also be identified in more complex MFIS and FeFET structures. Antiferroelectric-like characteristics observed for relatively high Si dopant concentration reveal significant trapping superimposed onto the ferroelectric memory window limiting the general program/erase endurance of the devices to 104 cycles. In addition, worst case disturb scenarios for a VDD/2 and VDD/3 scheme are evaluated to prove the viability of one-transistor memory cell concepts. The ability to tailor the ferroelectric properties by appropriate dopant concentration reveals disturb resilience up to 106 disturb cycles while maintaining an ION to IOFF ratio of more than four orders of magnitude.

Effects of Mg-Doping on ${\rm HfO}_{2}$-Based ReRAM Device Switching Characteristics

We report the switching characteristics of Mg-doped HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based ReRAM devices consisting of Ru/ Mg:HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiN/W stacks. The concentration of the Mg dopant was varied from 0% to 20% for four samples to show the impact on the forming voltage. In addition to reducing the forming voltage from 2.8 to 1.7 V, Mg doping in HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> also improved the repeatability in the initial device characteristics, switching characteristics, and retention. The mechanism of conduction was identified as Frenkel-Poole emission in doped and undoped samples in virgin resistance state (VRS). Further analysis showed that the increased conductance in the doped samples in VRS was due to higher carrier concentration.

Complementary Role of Field and Temperature in Triggering ON/OFF Switching Mechanisms in ${\rm Hf}/{\rm HfO}_{2}$ Resistive RAM Cells

We present an investigation on the role of temperature and electric field as driving forces in the initiation of the resistive switching processes. The impact of temperature in both on- and off-states is analyzed in detail, using an electrothermal numerical model formulation. dc and pulsed temperature-dependent data, collected on scaled crossbar test structure cells, serially connected with an on-chip control transistor, are used to extract material information and are furthermore analyzed in conjunction with model outputs. With these results, further discussion is presented, suggesting points of attention for scaled cell design in the below-10-nm realm.

Low-Frequency Noise Characteristics for Various ${\rm ZrO}_{2}$-Added ${\rm HfO}_{2}$-Based 28-nm High-$k$/Metal-Gate nMOSFETs

In this letter, the effect of adding ZrO2 to different positions in an HfO2-based high-k (HK) gate-stack is investigated by a low-frequency (1/ f ) noise measurement. The tested nMOSFETs are fabricated using 28-nm gate-last HK/metal-gate technology with a ~ 1-nm SiO2 interfacial layer. The 1/f noise mechanism of these devices is described by the carrier number fluctuation, and the extracted trap densities (Nt)are 8.9 × 1018-5.1 × 1019 eV-1 cm-3. However, reference devices with a pure ZrO2 gate dielectric exhibit 1/f noise characteristics that are consistent with the unified model, which incorporates both the carrier number and the correlated mobility fluctuations. The reference devices are with lower Nt values in the range of 5.8 × 1017-2.4 × 1018 eV-1 cm-3. In addition, there is an increase in Nt as the initial HfO2 layer becomes thicker.These results show that the trapping behavior is mainly dominated by the HfO2 film and is dependent on the thickness of the initial HfO2 layer in the ZrO2/HfO2/SiO2gate-stack.

High Polarization and Low-Repulsion ${\rm HfO}_{2}$ Thin Film for Alkali Metal Ion Detections by Plasma System With a Complementary Filter

A new plasma system with a complementary filter for low-damage carbon tetrafluoride $({\rm CF}_{4})$ plasma treatment is proposed to incorporate fluorine (F) atoms into a hafnium dioxide $({\rm HfO}_{2})$ thin-film sensing membrane in an electrolyte-insulator-semiconductor structure for alkali metal ion ( ${\rm Na}^{+}$ and ${\rm K}^{+}$ ) detection. Hf 4f and F 1s X-ray photoelectron spectra confirmed the incorporation of fluorine (F) atoms into the ${\rm HfO}_{2}$ sensing membrane after low-damage ${\rm CF}_{4}$ plasma treatment. As the duration of the plasma treatment is increased, the F 1s intensity and the amount of Hf–F bonds increased, and the corresponding ${\rm Na}^{+}$ and ${\rm K}^{+}$ sensitivities drastically increased (pNa: 121.6 mV/pNa; pK: 98.1 mV/pK). The super-Nernst phenomenon is attributed not only to the formation of higher dipole property between Hf and F than that between Hf and O but also to the reduction of plasma bombardment and UV irradiation, which damage the ${\rm HfO}_{2}$ sensing membrane. A positive charge model is proposed to explain the improvements by fluorine incorporation with complementary filter.

Cycle-to-Cycle Intrinsic RESET Statistics in ${\rm HfO}_{2}$-Based Unipolar RRAM Devices

The statistics of the RESET voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ) and the RESET current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ) of Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt resistive random access memory (RRAM) devices operated under unipolar mode are analyzed. The experimental results show that both the distributions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are strongly influenced by the distribution of initial resistance in the ON state ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ), which is related to the size of the conductive filament (CF) before RESET. By screening the statistical data into different resistance ranges, both the distributions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are shown to be compatible with a Weibull model. Contrary to previous reports for NiO-based RRAM, the Weibull slopes of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are demonstrated to be independent of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . This is an indication that the RESET point, defined in this letter as the point of maximum current, corresponds to the initial phase of CF dissolution. On the other hand, given that the scale factor of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> distribution ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET63%</sub> ) is roughly independent of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> , the scale factor of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET63%</sub> ) is inversely proportional to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . This is analogous to what was found in NiO-based RRAM and it is consistent with the thermal dissolution model of RESET. Our results highlight the intrinsic link between the SET and RESET statistics and the need for controlling the variation of ON-state resistance to reduce the variability of the RESET voltage and current.

Modeling the Impact of Reset Depth on Vacancy-Induced Filament Perturbations in ${\rm HfO}_{2}$ RRAM

Random telegraph noise in resistive switching memory devices is governed by two distinct mechanisms-oxygen vacancy perturbations in the filament as well as the electron trapping-detrapping phenomenon. In this letter, we focus on the dominant role of vacancies in governing the stability of the filament in the high resistance state and characterize the dependence of the read disturb voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DIST</sub> ) on the depth of the reset level during switching. Our slow voltage ramp read disturb tests at different reset levels indicate the possibility of filamentary instability even for read voltages lower than the standard value of 0.10 V. These experimental trends can be well explained using the quantum point contact model for conduction in the filament, as deeper reset levels induce very steep potential gradients at the two ends of the constriction that make the filaments highly unstable and susceptible to structural modifications due to vacancy generation and/or transport during memory read operation.

Improvement of the Anneal-Induced Valence Band Offset Variation by the Hybrid Deposition of ${\rm HfO}_{2}$ on Si

Controlling threshold voltage variation during fabrication is essential, and one source for the variation is the thermal instability of valence band offset (VBO) for HfO2 deposited on Si. It has been reported that VBO can be changed as much as 0.33-0.60 eV after annealing. This paper proposes a hybrid process with both H2O and ozone as oxygen source during the deposition of HfO2 film. X-ray photoelectron spectroscopy shows that the VBO of this hybrid-fabricated film changes as little as 0.02 eV after a 600 °C anneal, which is compatible with the gate-last process. The improved stability is further confirmed by the VFB extracted from the C-V measurement. The physical processes that may be responsible for this improvement are discussed.

Performance Enhancement on p-Channel Charge-Trapping Flash Memory Device With Epitaxial Si/Ge Super-Lattice Channel

Operation characteristics of p-channel ${\rm TaN}/{\rm Al}_{2}{\rm O}_{3}/{\rm HfO}_{2}/{\rm HfAlO}_{2}/{\rm SiO}_{2}/{\rm Si}$ MAHOS-type nonvolatile memory devices with an epitaxial Si/Ge super-lattice (SL) channel are investigated in this letter, where the SL channel is characterized with good crystal structure and high thermal stability. Remarkable improvement on programming and erasing speeds is observed, as compared to those with SiGe channel. Furthermore, the degradation on reliability properties of retention and endurance is negligible for the device with employing a SL channel.

Comparison of Charge Pumping and &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;$1/f$&lt;/tex&gt; &lt;/formula&gt; Noise in Irradiated Ge pMOSFETs

Irradiated Ge pMOSFETs have been characterized via charge pumping ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CP</sub> ) and 1/ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> noise. The noise increases much more with irradiation than does <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CP</sub> for devices with eight Si monolayers at the interface, while devices with five Si monolayers and lower halo implantation dose exhibit comparable increases in noise and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CP</sub> with irradiation. These results suggest that border traps in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> affect the noise more than interface traps, and that devices with eight Si monolayers have a higher border-trap density than devices with five Si monolayers. Noise measurements as a function of gate voltage show that the border trap density increases significantly toward the Ge valence band edge, while three-level charge pumping reveals an interface trap density that increases slightly toward midgap.

Effects of Metal Gates and Back-End-of-Line Materials on X-Ray Dose in ${\rm HfO}_{2}$ Gate Oxide

The effects of 10-keV and 400-keV endpoint-energy bremsstrahlung x-rays have been studied using the Monte Carlo simulator, MRED, for MOS capacitors with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics and TiN and TaN metal gates. We compute the reduction in dose that occurs for 10-keV x-ray irradiation of thin HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics sandwiched between the metal gate and the Si substrate. We quantify the effects of back-end-of-line metallization layers, including copper interconnects, W vias, and borophosphosilicate glass (BPSG) and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> passivation layers for low and medium energy x-rays. For thick metallization stacks irradiated by 10-keV x-rays, dose enhancement or attenuation can occur, depending on material type and overlayer thicknesses. For similar stacks irradiated with 400-keV endpoint-energy bremsstrahlung x-rays, significant dose enhancement is observed.

Investigation of Surface Sputtering and Post Annealing Effects on Atomic Layer Deposited ${\rm HfO}_{2}$ and ${\rm TiO}_{2}$

Tetrakis (diethylamino) hafnium and tetrakis (diethylamino) titanium were used for the atomic layer deposition (ALD) of HfO2 and TiO2 films on silicon (100) substrates with water being the oxidant. Studies on the decomposition temperatures of both metal precursors within the reactor and on carbon impurity helped determine the optimal ALD temperature range. X-ray photoelectron spectroscopy showed that after a short Ar+ sputtering to remove surface contaminants, both HfO2 and TiO2 were carbon-free when films were deposited within the optimal ALD temperature window. However, Ar+ sputtering of the surface altered the chemical state of Ti4+ and led to the formation of lower oxidation states of titanium. Optical profiling in the phase-shifting interferometry mode and grazing incidence X-ray diffraction were applied to probe the change of surface morphology and film crystallinity upon post-deposition annealing at 600°C for 5 min. Capacitance-voltage and current-voltage measurements were performed over a metal-insulator-semiconductor structure after electron beam evaporation of 150-nm-thick Al metal contacts on the dielectric layers; the calculated dielectric constant, k, of TiO2 was found to be about three times higher than that of HfO2 and the measured leakage current densities for both metal oxides were below 2 × 10-5 A/cm2 at 1-V.

Total Ionizing Dose Effects on Strained ${\rm HfO}_{2}$-Based nMOSFETs

Radiation-induced charge trapping and mobility degradation are measured on uniaxially stressed HfO2-based nMOSFETs. Controlled external mechanical stress is applied via a four-point bending jig while the samples are irradiated using 10-keV X-rays. Positive charge trapping is observed for unstressed devices, and for devices irradiated under both compressive and tensile stress. Reduced trapped charge is measured as the uniaxial stress level increases. These results suggest that the increased stress leads to a reconfiguration of defect microstructure, as compared to the unstressed devices. The reconfiguration consists of changes in bond lengths and angles and a corresponding change in trap energy levels, which can (1) reduce the probability that a defect can capture holes, (2) increase the probability for electron and trapped-hole recombination, and/or (3) increase the mobility of the transporting holes in the oxides of the devices that are irradiated under stress. These results show that increased mechanical stress in high-k dielectrics does not degrade their radiation hardness. We also observe that the post-irradiation channel mobility degrades less in uniaxially stressed devices than unstressed devices.

Radiation Induced Charge Trapping in Ultrathin ${\rm HfO}_{2}$-Based MOSFETs

Radiation induced charge trapping in ultrathin HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based n-channel MOSFETs is characterized as a function of dielectric thickness and irradiation bias following exposure to 10 keV X-rays and/or constant voltage stress. Positive and negative oxide-trap charges are observed, depending on irradiation and bias stress conditions. No significant interface-trap buildup is found in these devices under these irradiation and stress conditions. Enhanced oxide-charge trapping occurs in some cases for simultaneous application of constant voltage stress and irradiation, relative to either type of stress applied separately. Room temperature annealing at positive bias after irradiation of transistors with thicker gate dielectric films leads to positive oxide-trapped charge annihilation and/or neutralization in these devices, and net electron trapping. The oxide thickness dependence of the radiation response confirms the extreme radiation tolerance of thin HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric layers of relevance to device applications, and suggests that hole traps in the thicker layers are located in the bulk of the dielectric. A revised methodology is developed to estimate the net effective charge trapping efficiency, f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ot</sub> , for high-kappa dielectric films. As a result, estimates of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ot</sub> for Hf silicate capacitors and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> transistors in previous work are reduced by up to 18%.