Transmission Line Measurements Research Articles

The Effects of a Gate Bias Condition on 1.2 kV SiC MOSFETs during Irradiating Gamma-Radiation.

We investigated the effects of gate bias regarding the degradation of electrical characteristics during gamma irradiation. Moreover, we observed the punch through failure of 1.2 kV rated commercial Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) due to the influence of gate bias. In addition, the threshold voltage (VT) and on-resistance (Ron) of the SiC MOSFETs decreased significantly by the influence of gate bias during gamma irradiation. We extracted the concentration of carriers and fixed charge (QF) in oxide using N-type SiC MOS capacitors and Transmission Line Measurement (TLM) patterns to analyze the effects of gamma irradiation. The Total Ionizing Dose (TID) effect caused by high-energy gamma-ray irradiation resulted in an increase in the concentration of holes and QF in both SiC and oxide. To analyze the phenomenon for increment of hole concentration in the device under gate bias, we extracted the subthreshold swing of SiC MOSFETs and verified the origin of TID effects accelerated by the gate bias. The QF and doping concentration of p-well values extracted from the experiments were used in TCAD simulations (version 2022.03) of the planar SiC MOSFET. As a result of analyzing the energy band diagram at the channel region of 1.2 kV SiC MOSFETs, it was verified that punch-through can occur in 1.2 kV SiC MOSFETs when the gate bias is applied, as the TID effect is accelerated by the gate bias.

Characterization of Mn5Ge3 Contacts on a Shallow Ge/SiGe Heterostructure.

Mn5Ge3 is a ferromagnetic phase of the Mn-Ge system that is a potential contact material for efficient spin injection and detection. Here, we investigate the creation of Mn5Ge3-based contacts on a Ge/SiGe quantum well heterostructure via solid-state synthesis. X-ray diffraction spectra fitting indicates the formation of Mn5Ge3-based contacts on bulk Ge and Ge/SiGe. High-resolution scanning transmission electron microscopy imaging and energy dispersive X-ray spectroscopy verify the correct Mn5Ge3-based phase formation. Schottky diode measurements, transmission line measurements, and Hall measurements reveal that Mn5Ge3-based contacts serve as good p-type contacts for Ge/SiGe quantum well heterostructures due to having a low Schottky barrier height of 0.10eV (extracted from a Mn5Ge3/n-Ge analogue) and a contact resistance in the order of 1 kΩ. Furthermore, we show that these electrical characteristics have a gate-voltage dependence, thereby providing tunability.

Single-Ended Time Domain Fault Location Based on Transient Signal Measurements of Transmission Lines

Single-Ended Time Domain Fault Location Based on Transient Signal Measurements of Transmission Lines

Measuring the permittivity of fused silica with planar on-wafer structures up to 325 GHz

Fused silica has become an interesting alternative to silicon for millimeter-wave (mmWave) applications. Unfortunately, there are a few reports on the measurement of fused silica's permittivity above 110 GHz that use electrical rather than optical methods. Given that mmWave applications use electrical circuits, additional electrical data would be useful to industry. To test the feasibility of electrical methods, we applied on-wafer techniques based on coplanar waveguide transmission lines to measure the complex permittivity of fused silica to 325 GHz. Our approach used the multiline thru-reflect-line algorithm on the scattering parameter measurements of transmission lines. Our method combined these results with dc measurements of the resistivity of the metals, simulations of the coplanar waveguide cross section, and dimensional metrology. In short, our measurements do not show significant dielectric dispersion for fused silica up to 325 GHz. The resulting complex permittivity was ϵr=3.87±0.03 and a loss tangent tanδ< 0.005 from 320 MHz to 325 GHz. To support our conclusions, we performed an uncertainty analysis considering relevant sources of uncertainty. In the broader context, these results show that fused silica is a suitable substrate for mmWave electronics where the loss tangent must be less than 0.005 up to 325 GHz.

Boosting the performance of low‐cost eco‐friendly pyramidal absorbers with a Salisbury screen

AbstractInstead of using expensive highly performing conventional pyramidal absorbers, in some cases, the use of absorbers based on very cheap eco‐friendly materials is an attractive alternative. The authors introduce a novel technique to improve the absorption bandwidth of these intrinsically low‐quality absorbers by adding a Salisbury screen at the base of the pyramidal absorber, which adds two extra design parameters. The first is the resistive sheet surface impedance, and the second is the resonance frequency of the Salisbury screen. By tuning these two parameters, better impedance matching can be obtained. This is verified with the help of a transmission line model, full‐wave simulations, and measurements. The method is applied to two different lower‐quality absorbers found in the literature. In the first absorber, the operating bandwidth is increased at the lower frequency side by 40%, and in the second one, this is about 90%. Finally, a prototype of an eco‐friendly combined absorber is designed and fabricated. The measurement validates the expected behaviour.

A cascaded high-voltage high-frequency linear amplifier for power transmission line measurement

In this paper, a high-frequency and high-voltage linear cascaded amplifier based on parallel optical fiber isolation is proposed. The electro-optical synchronous drive of the excitation signal is realized through equal proportional laser splitting, which achieves the same linear gain and output phase shift in each photoelectric conversion unit. The differential linear cascade topology designed in this paper effectively solves the gain bandwidth product limitation and achieves a high-voltage linear output in a high-frequency range. The new amplifier solves the problem that due to the low AC excitation voltage of traditional impedance analyzer, the signal attenuation is severe in long distance and high insulation distributed electrical parameter network. It can be widely used to measure high-frequency dielectric loss and impedance spectrum for dielectric materials and electrical components in industry and laboratory. By cascading n-stage amplifier units, the voltage gain can reach 6n times. Finally, a 16-stage cascade amplifier is built, and the response characteristics are tested with the distributed electrical parameter network loads. The output characteristics show that the expected amplifier gain can be obtained accurately in the high-frequency range of 100 kHz–100 MHz, the output voltage can reach 192Vpp, and the peak current can reach ±500 mA. The maximum of the curve about THD and noise versus frequency could be limited to 0.49 %, which could meet the needs of on-site measurement.

Low contact resistance of NiGeSn on n-GeSn

A systematic investigation of the NiGeSn formation and its contact resistivity with GeSn semiconductors are studied. The method of investigation is based on the circular transmission line measurement (CTLM) geometry. The optimum NiGeSn formation temperature is 325 °C, offering a lower contact resistivity of 4.15 × 10−5 Ω·cm2 on n-GeSn. The elemental diffusion mechanism during the NiGeSn formation is also discussed. In line with the research of new materials for cryogenic electronics, GeSn shows a low contact resistivity of 1.79 × 10−5 Ω·cm2 at 5 K. These findings offer valuable insights into optimizing GeSn-based contact technologies for both low-power and cryogenic applications.

(Invited) NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 Heterojunction Lateral Rectifiers with Reverse Breakdown Voltage > 7kV

There is significant recent interest in development of Ga2O3 power devices due to their capability for high temperature operation, reduced on-state and switching losses due to lower on-resistance for high voltage devices, and potentially higher frequency switching capability. These are targeted for renewable energy transmission systems, electric vehicle (EV) traction inverter and motor control systems, fast charging stations and more electric aircraft. Since the efficiency of EV powertrain inverters is partially determined by the efficiency of the switching transistors, it is of interest to examine ultra-wide-bandgap semiconductor electronics. The successful development of these power transistors is expected to significantly increase the longevity of a battery charge and the resultant cost of an EV.In this work, NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 heterojunction lateral geometry rectifiers with diameter 50-100 µm exhibited maximum reverse breakdown voltages >7kV, showing the advantage of increasing the bandgap using the β-(Al x Ga1-x )2O3 alloy. This Si-doped alloy layer was grown by Metal Organic Chemical Vapor Deposition with an Al composition of ~20%. On state resistances were in the range 50-2180 Ω.cm2, leading to power figures-of-merit up to 0.72 MW.cm-2. The forward turn-on voltage was in the range 2.3-2.5 V, with maximum on/off ratios >700 when switching from 5V forward to reverse biases up to -100V. Transmission line measurements showed the specific contact resistance was 0.12 Ω.cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based device. Figure 1

Significant effect of thin oxide layer on characteristics of p-InGaN/GaN nonalloyed ohmic contacts

In an interconnected high-vacuum illustration system, the surfaces of p-InGaN/GaN heterostructures grown with integrated metalorganic chemical vapor deposition were treated in O2 gas for different times at room temperature and then transferred to another chamber for fabricating ohmic contacts via sputtering Pd/Pt/Au multi-layers. X-ray photoelectron spectroscopy measurements unveil that the proportions of Ga–O of the treated samples significantly increase compared with that of the as-grown sample, indicating that a thin layer of GaOx forms on the p-InGaN/GaN surface after exposing to oxygen or air atmospheres. Meanwhile, the samples exposed to O2 or air were found to have much higher specific contact resistance, i.e., higher by two orders of magnitude than that of the as-grown sample. The specific contact resistance of the as-grown sample was derived as 9.3 × 10−5 Ω cm2 using the circular transmission line measurement. Furthermore, the Schottky barrier height of the samples was determined from the measured I–V curves with the thermionic field emission model and was revealed to be closely related to surface treatments. Despite the fact that the insulating layer of GaOx was as thin as 1.2–1.4 Å for the samples exposed to oxygen at room temperature, it can act as an extra barrier layer causing significant increase in the specific contact resistance via blocking the tunneling of carriers. Therefore, the effective removal of p-InGaN surface oxide plays a vital role in preparing good ohmic contacts.

A Hybrid EMC Testing Facility: Combining Transmission Line and Reverberation Chamber Measurement System

By combining a transmission line system (TLS) and a reverberation chamber (RC), a hybrid electromagnetic compatibility (EMC) testing facility is designed and constructed. Generally, the lowest usable frequency (LUF) of an RC is limited by its dimension, which limits the application of RCs for EMC testing at low frequencies. Therefore, to improve the field uniformity (FU) of an RC at frequencies lower than the LUF, a TLS is integrated into the RC. After optimizing the load resistance, length, and width of the TLS, the resonant frequency and electric field spikes of the hybrid system are eliminated. The FU of the E-field in the system is greatly improved in the frequency range of 0-30 MHz. Moreover, using an oscillating wall stirrer in the RC, the FU satisfies the standard (IEC 61000-4-21) above 80 MHz. Results show that combining the TLS and the RC testing system could be widely used for EMC testing in the frequency range of 0-30 MHz and 80 MHz-6 GHz.

AlGaN/GaN heterostructures for high power and high-speed applications

Abstract AlGaN/GaN heterostructures are one of the most promising semiconducting structures for fabricating high-speed and high-power electronic devices such as high electron mobility transistors and heterojunction bipolar transistors. Due to the lack of native substrates, these epitaxial structures are generally grown on foreign substrate materials such as sapphire, SiC and Si by using two-step growth techniques. In this paper, a few test structures along with TLM pads, FET structure, ohmic contacts and Schottky contacts have been fabricated on AlGaN/GaN heterostructure by photolithography, reactive ion etching, and e-beam metallization. Transmission line measurement has been used to calculate the sheet resistivity and contact resistance of ohmic pads. Current voltage measurement is used to test an FET structure of size 1 × 150 µm2 with a gate length of 4 µm and source to drain spacing of 5 µm.

(Invited) NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 Heterojunction Lateral Rectifiers with Reverse Breakdown Voltage > 7kV

NiO/ β-(Al x Ga1-x )2O3 /Ga2O3 heterojunction lateral geometry rectifiers with diameter 50-100 µm exhibited maximum reverse breakdown voltages >7kV, showing the advantage of increasing the bandgap using the β-(Al x Ga1-x )2O3 alloy. This Si-doped alloy layer was grown by Metal Organic Chemical Vapor Deposition with an Al composition of ~21 %. On state resistances were in the range 50-2180 Ω.cm2, leading to power figures-of-merit up to 0.72 MW.cm-2. The forward turn-on voltage was in the range 2.3-2.5 V, with maximum on/off ratios >700 when switching from 5V forward to reverse biases up to -100V. Transmission line measurements showed the specific contact resistance was 0.12 Ω.cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based rectifier.

Strain Monitoring of Overhead Transmission Line Based on Brillouin Scattering

The change in the optical fiber state and the status of transmission line often leads to the change of strain in its composite optical fiber. This paper attempts to use a commercial BOTDR (Brillouin optical time-domain reflectometry) to monitor the strain of optical fiber composited in transmission line. The Brillouin spectra of typical optical fiber used in the transmission line are measured by a commercial BOTDR at room temperature, the spectra are fitted and the key parameters are calculated, and then the strain along whole optical fiber is obtained by demodulation. The results show that BOTDR can effectively monitor the optical fiber strain, and the mean standard deviation of strain measured for multiple measurements under the same condition is only about 8 με, which can stastify the requirements of practical cases. The work of this paper lays a foundation for the strain measurement of transmission line.

NiO/β-(AlxGa1−x)2O3/Ga2O3 heterojunction lateral rectifiers with reverse breakdown voltage >7 kV

NiO/β-(AlxGa1−x)2O3/Ga2O3 heterojunction lateral geometry rectifiers with diameter 50–100 μm exhibited maximum reverse breakdown voltages >7 kV, showing the advantage of increasing the bandgap using the β-(AlxGa1−x)2O3 alloy. This Si-doped alloy layer was grown by metal organic chemical vapor deposition with an Al composition of ∼21%. On-state resistances were in the range of 50–2180 Ω cm2, leading to power figures-of-merit up to 0.72 MW cm−2. The forward turn-on voltage was in the range of 2.3–2.5 V, with maximum on/off ratios >700 when switching from 5 V forward to reverse biases up to −100 V. Transmission line measurements showed the specific contact resistance was 0.12 Ω cm2. The breakdown voltage is among the highest reported for any lateral geometry Ga2O3-based rectifier.

Impedance modeling for excluding contact resistance from cross-plane electronic conductivity measurement of anisotropic two-dimensional Ti3C2Tx MXenes

We propose impedance spectroscopy modeling as a convenient tool for estimating the cross-plane conductivity of anisotropic two-dimensional materials by excluding contact resistance with the underlying metal electrodes. We showcase this idea on two types of titanium carbide Ti3C2Tx MXenes, wherein Tx represents surface functional termination. These MXenes are synthesized from the same parent MAX phase material (Ti3AlC2) by different synthesis protocols and are studied in their plain as-synthesized states as well as after short annealing. The cross-plane conductivity of MXenes estimated by our approach appears to be up to an order of magnitude higher than is estimated by a conventional one. We validate our impedance modeling approach by comparing the specific contact resistance results derived from it to a direct estimation by transmission line measurement. We also deduce which functional group has a dominant footprint on the conductivity in each studied MXene by performing numerical simulations on cross-plane conductivity as well as on electronic band structures. The novel equivalent circuit developed herein may be extended to other anisotropic thin films to aid their application in various electronic devices.

Effect of Rapid Thermal Annealing Conditions on the Specific Resistance of the Ohmic Contacts of Ti/Al/Ni/Au Metallization to the GaN/AlGaN Heterostructure

Effect of rapid thermal annealing conditions on the specific resistance of the ohmic contacts of Ti/Al/Ni/Au metallization with layer thicknesses of 20/120/40/40 nm to the GaN/AlGaN heterostructure with a two-dimensional electron gas on a sapphire substrate has been discovered by transmission line measurement. Rapid thermal annealing of the samples was carried out by the contact heating from the sapphire substrate side in a nitrogen atmosphere at the temperature range from 750 to 1000 °C for 30, 60, and 90 s. It has been discovered that the dependence of the specific contact resistance on the temperature contains two temperature optimums, at which the specific contact resistance of the ohmic contact is less than 1 ⋅ 10–4 Ohm⋅ cm2. The appearance of the first temperature optimum is due to the decrease of the distance from the diffusion front of the low-resistance layer of intermetallic compounds formed during the rapid thermal annealing of the Ti/Al/Ni/Au metallization to the region of the two-dimensional electron gas. Outside the first temperature optimum, an increase in the specific contact resistance of up to 9 ⋅ 10–3 Ohm⋅ cm2 is observed, due to the absorption of the AlGaN layer by a low-resistance layer of intermetallic compounds, which leads to the degradation of the two-dimensional electron gas under the contacts and deterioration of its conductive properties. The second temperature optimum is due to the passage of the diffusion front of the two-dimensional electron gas region and the establishment of a side contact between the low-resistance intermetallic layer and the two-dimensional electron gas, which leads to the decrease in the specific contact resistance. With an increase in the fast thermal annealing time from 30 to 90 s the shift of the interval of the first temperature optimum from 800 to 775 °C for the lower boundary and from 825 to 800 °C for the upper boundary, and for the second temperature optimum from 875 to 850 °C for the lower boundary, and from 950 to 875 °C for the upper boundary is observed, which is due to an equivalent increase in the diffusion depth of the Ti/Al/Ni/Au metallization components. The results obtained can be used in the technology for creating GaN-based products with a two-dimensional electron gas.

Determination of the Permittivity of Transmission Lines at Milli-Kelvin Temperatures

Many quantum technologies rely heavily on propagation of RF and microwave signals through devices at cryogenic temperatures, and detailed understanding of materials and signal propagation is therefore key to improving the performance of quantum circuits. The properties of dielectric substrate materials used for transmission lines (TLs) such as their permittivity need to be precisely determined to design high performance quantum integrated circuits. In this paper, we discuss a measurement technique for determining the effective permittivity of a TL at mK temperatures. The technique utilizes S-parameter measurements of multiple TLs to reliably extract the effective permittivity of the TL implemented in a substrate material. The technique is demonstrated using measured S-parameters of grounded co-planar waveguide (GCPW) at 296 K and 15 mK. The effective permittivity of the TL at 296 K and 15 mK are determined from measurements and compared. We observed the effective permittivity determinations at 15 mK to be approximately frequency independent and calculated the relative permittivity of Rogers RO4350B material at 15 mK to be 3.64. There is no significant deviation from this relative permittivity value with respect to manufacturer data and from measured data at 296 K.

Low Temperature Loss Measurement of Aluminium Thin Film Transmission Lines

Low Temperature Loss Measurement of Aluminium Thin Film Transmission Lines

Suppression of p-type parasitic channel formation at the interface between the aluminum nitride nucleation layer and the high-resistivity silicon substrate

In this study, GaN-based epitaxial structures were grown on high-resistivity silicon (HRSi) substrates by metalorganic chemical vapor deposition. The p-type parasitic channels generated at the interfaces of the aluminum nitride (AlN) nucleation layers and HRSi substrates were characterized by surface capacity measurement, backside secondary ion mass spectrometry, and spread resistance profiling. The 2-nm thick silicon nitride (SiNx) layer formed by nitridation on the HRSi substrates was used to suppress the Al diffusion from the 50-nm AlN nucleation layer and also prevented from generation of the p-type parasitic channels. The p-type parasitic channels induced insertion losses at high frequencies. Transmission line measurement was used to determine the insertion losses. The insertion loss of the GaN-based epitaxial structure with the optimized 25-nm AlN nucleation layer on the 2-nm SiNx layer was -2.72 dB/mm. It was only 0.04 dB/mm higher than that of the annealed HRSi substrate (-2.68 dB/mm) at 10 GHz. Obviously, the diffusion of Al from the optimized 25-nm thick AlN nucleation layer into the HRSi substrate can be alleviated by the SiNx layer, thereby reduced insertion loss.

Conductance anisotropy of MOCVD-grown α-Ga2O3 films caused by (010) β-Ga2O3 filament-shaped inclusions

A significant anisotropy in the electrical conductance was observed in Si-doped α-Ga2O3/sapphire samples grown via liquid-injection metal organic chemical vapor deposition. Additionally to epitaxial α-Ga2O3 diffraction, x-ray diffraction (XRD) revealed maxima related to (010) β-Ga2O3. Transmission electron microscopy, atomic force microscopy (AFM), and Raman spectroscopy of undoped samples with similar XRD pattern confirmed the formation of (010) β-Ga2O3 filaments in the epitaxial α-Ga2O3 film. In Si-doped samples, conductive AFM and temperature-dependent current–voltage measurement on transmission line measurement resistors confirmed, that β-Ga2O3 filaments were responsible for significantly higher conductivity along the α-Ga2O3 direction compared to [0001] α-Ga2O3 direction. Current–voltage measurements of transistor structures suggested semiconducting behavior of the β-Ga2O3 filaments embedded in the highly resistive α-Ga2O3 films.