Nonresonant Transmission Line Probe for Sensitive Interferometric Electron Spin Resonance Detection.

Electron spin resonance (ESR) spectroscopy measures paramagnetic free radicals, or electron spins, in a variety of biological, chemical, and physical systems. Detection of diverse paramagnetic species is important in applications ranging from quantum computation to biomedical research. Countless efforts have been made to improve the sensitivity of ESR detection. However, the improvement comes at the cost of experimental accessibility. Thus, most ESR spectrometers are limited to specific sample geometries and compositions. Here, we present a nonresonant transmission line ESR probe (microstrip geometry) that effectively couples high frequency microwave magnetic field into a wide range of sample geometries and compositions. The nonresonant transmission line probe maintains detection sensitivity while increasing availability to a wider range of applications. The high frequency magnetic field homogeneity is greatly increased by positioning the sample between the microstrip signal line and the ground plane. Sample interfacing occurs via a universal sample holder which is compatible with both solid and liquid samples. The unavoidable loss in sensitivity due to the nonresonant nature of the transmission line probe (low Q) is recuperated by using a highly sensitive microwave interferometer-based detection circuit. The combination of our sensitive interferometer and nonresonant transmission line provides similar sensitivity to a commercially available ESR spectrometer equipped with a high-Q resonator. The nonresonant probe allows for transmission, reflection, or dual-mode detection (transmission and reflection), where the dual-mode results in a √2 signal enhancement.

Survival after abdominal aortic aneurysm repair is affected by socioeconomic status.

OBJECTIVE: The association between socioeconomic status (SES) and outcome after abdominal aortic aneurysm (AAA) repair is largely unknown. This study aimed to determine the influence of SES on postoperative survival after AAA repair. METHODS: Patients undergoing surgical treatment of AAA at a tertiary referral center between January 1993 and July 2013 were retrospectively collected. Thirty-day postoperative mortality and long-term mortality were documented through medical record review and the Michigan Social Security Death Index. SES was quantified using the neighborhood deprivation index (NDI), which is a standardized and reproducible index used in research that summarizes eight domains of socioeconomic deprivation and is based on census tracts derived from patients' individual addresses. The association between SES and survival was studied by univariable and multivariable Cox regression analysis. RESULTS: A total of 767 patients were included. The mean age was 73 years; 80% were male, 77% were white, and 20% were African American. There was no difference in SES of patients who underwent open vs endovascular repair of AAA (P = .489). The average NDI was -0.18 (minimum, -1.47; maximum, 2.35). After adjusting for the variables that were significant on univariable analysis (age, medical comorbidities, length of stay, and year of surgery), the association between NDI and long-term mortality was significant (P = .021; hazard ratio, 1.21 [1.05-1.37]). CONCLUSIONS: Long-term mortality after AAA repair is associated with SES. Further studies are required to assess which risk factors (behavioral, psychosocial) are responsible for this decreased long-term survival in low SES patients after AAA repair.

Ferroelectricity in Polar Polymer-based FETs: A Hysteresis Analysis.

There is an increasing number of reports on polar polymer-based Ferroelectric Field Effect Transistors (FeFETs), where the hysteresis of the drain current - gate voltage (Id-Vg) curve is investigated as the result of the ferroelectric polarization effect. However, separating ferroelectric effect from many of the factors (such as charge injection/trapping and the presence of mobile ions in the polymer) that confound interpretation is still confusing and controversial. This work presents a methodology to reliably identify the confounding factors which obscure the polarization effect in FeFETs. Careful observation of the Id-Vg curves, as well as monitoring the Id-Vg hysteresis and flat band voltage shift as a function of temperature and sweep frequency identifies the dominant mechanism. This methodology is demonstrated using 15-nm thick high glass transition temperature polar polymer-based FeFETs. In these devices, room temperature hysteresis is largely a consequence of charge trapping and mobile ions, while ferroelectric polarization is observed at elevated temperatures. This methodology can be used to unambiguously prove the effect of ferroelectric polarization in FeFETs.

Analysis and Control of RRAM Overshoot Current.

To combat the large variability problem in RRAM, current compliance elements are commonly used to limit the in-rush current during the forming operation. Regardless of the compliance element (1R-1R or 1T-1R), some degree of current overshoot is unavoidable. The peak value of the overshoot current is often used as a predictive metric of the filament characteristics and is linked to the parasitic capacitance of the test structure. The reported detrimental effects of higher parasitic capacitance seem to support this concept. However, this understanding is inconsistent with the recent successes of compliance-free ultra-short pulse forming which guarantees a maximum peak overshoot current. We use detailed circuit analysis and experimental measurements of 1R-1R and 1T-1R structures to show that the peak overshoot is independent of the parasitic capacitance while the overshoot duration is strongly dependent on the parasitic capacitance. Forming control can be achieved, in ultra-short pulse forming, since the overshoot duration is always less than the applied pulse duration. The demonstrated success of ultra-short pulse forming becomes easier to reconcile after identifying the importance of overshoot duration.

Wafer-Level Electrically Detected Magnetic Resonance: Magnetic Resonance in a Probing Station.

We report on a novel semiconductor reliability technique that incorporates an electrically detected magnetic resonance (EDMR) spectrometer within a conventional semiconductor wafer probing station. EDMR is an ultrasensitive electron paramagnetic resonance technique with the capability to provide detailed physical and chemical information about reliability limiting defects in semiconductor devices. EDMR measurements have generally required a complex apparatus, not typically found in solid-state electronics laboratories. The union of a semiconductor probing station with EDMR allows powerful analytical measurements to be performed within individual devices at the wafer level. Our novel approach replaces the standard magnetic resonance microwave cavity or resonator with a small non- resonant near field microwave probe. Using this new approach we have demonstrated bipolar amplification effect and spin dependent charge pumping in various SiC based MOSFET structures. Although our studies have been limited to SiC based devices, the approach will be widely applicable to other types of MOSFETs, bipolar junction transistors, and various memory devices. The replacement of the resonance cavity with the very small non- resonant microwave probe greatly simplifies the EDMR detection scheme and allows for the incorporation of this powerful tool with a wafer probing station. We believe this scheme offers great promise for widespread utilization of EDMR in semiconductor reliability laboratories.

Impact of RRAM Read Fluctuations on the Program-Verify Approach.

The stochastic nature of the conductive filaments in oxide-based resistive memory (RRAM) represents a sizeable impediment to commercialization. As such, program-verify methodologies are highly alluring. However, it was recently shown that program-verify methods are unworkable due to strong resistance state relaxation after SET/RESET programming. In this paper, we demonstrate that resistance state relaxation is not the main culprit. Instead, it is fluctuation-induced false-reading (triggering) that defeats the program-verify method, producing a large distribution tail immediately after programming. The fluctuation impact on the verify mechanism has serious implications on the overall write/erase speed of RRAM.

Rapid and Accurate C-V Measurements.

We report a new technique for the rapid measurement of full capacitance-voltage (C-V) characteristic curves. The displacement current from a 100 MHz applied sine-wave, which swings from accumulation to strong inversion, is digitized directly using an oscilloscope from the metal-oxide-semiconductor (MOS) capacitor under test. A C-V curve can be constructed directly from this data but is severely distorted due to non-ideal behavior of real measurement systems. The key advance of this work is to extract the system response function using the same measurement set-up and a known MOS capacitor. The system response correction to the measured C-V curve of the unknown MOS capacitor can then be done by simple deconvolution. No de-skewing and/or leakage current correction is necessary, making it a very simple and quick measurement. Excellent agreement between the new fast C-V method and C-V measured conventionally by an LCR meter is achieved. The total time required for measurement and analysis is approximately 2 seconds, which is limited by our equipment.

Electron spin resonance scanning probe spectroscopy for ultrasensitive biochemical studies.

Electron spin resonance (ESR) spectroscopy's affinity for detecting paramagnetic free radicals, or spins, has been increasingly employed to examine a large variety of biochemical interactions. Such paramagnetic species are broadly found in nature and can be intrinsic (defects in solid-state materials systems, electron/hole pairs, stable radicals in proteins) or, more often, purposefully introduced into the material of interest (doping/attachment of paramagnetic spin labels to biomolecules of interest). Using ESR to trace the reactionary path of paramagnetic spins or spin-active proxy molecules provides detailed information about the reaction's transient species and the label's local environment. For many biochemical systems, like those involving membrane proteins, synthesizing the necessary quantity of spin-labeled biomolecules (typically 50 pmol to 100 pmol) is quite challenging and often limits the possible biochemical reactions available for investigation. Quite simply, ESR is too insensitive. Here, we demonstrate an innovative approach that greatly enhances ESR's sensitivity (>20000× improvement) by developing a near-field, nonresonant, X-band ESR spectrometric method. Sensitivity improvement is confirmed via measurement of 140 amol of the most common nitroxide spin label in a ≈593 fL liquid cell at ambient temperature and pressure. This experimental approach eliminates many of the typical ESR sample restrictions imposed by conventional resonator-based ESR detection and renders the technique feasible for spatially resolved measurements on a wider variety of biochemical samples. Thus, our approach broadens the pool of possible biochemical and structural biology studies, as well as greatly enhances the analytical power of existing ESR applications.

Influence of Limb Position on Venous Blood Flow After Total Knee Arthroplasty: A Prospective Randomized Study.

Previous studies have suggested a clinical advantage when placing the limb in flexion after total knee arthroplasty (TKA). We sought to measure venous flow compared with control values after TKA. Our hypothesis was that the knee flexed positioning would not adversely affect venous flow. Two cohorts were prospectively evaluated. First, volunteers were randomized to positions with the knee flexed to approximately 90° or placed in a fully extended (control) position. Venous flow velocity was measured in the femoral vein every 15 minutes for 2 hours. Subsequently, 32 patients were randomized to 1 of these 2 positions after TKA, and venous flow velocity was measured in both the operative and the contralateral limb. In the healthy volunteer cohort, mean venous flow velocity was significantly higher at all time points in the flexion group compared with the extended control group (P<.05). After TKA, mean flow velocity for an extended knee (control) was 28.5 cm/s. Mean flow velocity for the flexed knee, foot-dependent group was 47.2 cm/s (P=.036) and for the flexed knee, foot-elevated group was 30.4 cm/s (P=.618). Placing the limb in a flexed position after TKA is not detrimental to venous flow velocity and resulted in higher velocities relative to the extended position. Placing the limb at 90° flexion does not cause venous stasis and should not increase the risk of deep venous thrombosis. [Orthopedics. 2023;46(1):8-12.].

Slow- and rapid-scan frequency-swept electrically detected magnetic resonance of MOSFETs with a non-resonant microwave probe within a semiconductor wafer-probing station.

We report on a novel electron paramagnetic resonance (EPR) technique that merges electrically detected magnetic resonance (EDMR) with a conventional semiconductor wafer probing station. This union, which we refer to as wafer-level EDMR (WL-EDMR), allows EDMR measurements to be performed on an unaltered, fully processed semiconductor wafer. Our measurements replace the conventional EPR microwave cavity or resonator with a very small non-resonant near-field microwave probe. Bipolar amplification effect, spin dependent charge pumping, and spatially resolved EDMR are demonstrated on various planar 4H-silicon carbide metal-oxide-semiconductor field-effect transistor (4H-SiC MOSFET) structures. 4H-SiC is a wide bandgap semiconductor and the leading polytype for high-temperature and high-power MOSFET applications. These measurements are made via both "rapid scan" frequency-swept EDMR and "slow scan" frequency swept EDMR. The elimination of the resonance cavity and incorporation with a wafer probing station greatly simplifies the EDMR detection scheme and offers promise for widespread EDMR adoption in semiconductor reliability laboratories.

Observation of Strong Reflection of Electron Waves Exiting a Ballistic Channel at Low Energy.

Wave scattering by a potential step is a ubiquitous concept. Thus, it is surprising that theoretical treatments of ballistic transport in nanoscale devices, from quantum point contacts to ballistic transistors, assume no reflection even when the potential step is encountered upon exiting the device. Experiments so far seem to support this even if it is not clear why. Here we report clear evidence of coherent reflection when electron wave exits the channel of a nanoscale transistor and when the electron energy is low. The observed behavior is well described by a simple rectangular potential barrier model which the Schrodinger's equation can be solved exactly. We can explain why reflection is not observed in most situations but cannot be ignored in some important situations. Our experiment also represents a direct measurement of electron injection velocity - a critical quantity in nanoscale transistors that is widely considered not measurable.