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In this letter, the current limiters fabricated by the gallium nitride (GaN) active epitaxial layers are introduced to achieve GaN-based robust low-noise amplifiers (LNAs). In principle, by taking advantage of the current saturation effect, the gate dc current which causes gate degradation or breakdown can be controlled below the breakdown limit at any input level. The active current limiter can also reduce the ON-state degradation by reducing the drain current. Two designs of robust LNAs in the Ka-band are presented. The LNA1 has current limiters in gate regions, and the LNA2 has current limiters in both gate and drain regions. Both LNAs survive in a 1-h stress experiment with 32–30.5-dBm input power. After the stress experiment, both LNAs show little degradation in noise figure, and the LNA2 shows little degradation in gain because of the drain current limiter. [ABSTRACT FROM AUTHOR]

Reduction of the reverse leakage current is critical to AlGaN/GaN heterostructures in high power and high frequency applications. Taking AlGaN/GaN Schottky barrier diodes (SBDs) as an example, we demonstrate both theoretically and experimentally that low-fluence neutron irradiation can be a promising way to reduce the reverse leakage current while maintaining other electronic properties almost unchanged. A clear physical picture is given to elucidate the mechanism, which includes three main scenarios: (i) in pre-irradiated AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates, the configuration of threading dislocations (DLs) is the mixture of pure DLs and DLs decorated by group-III vacancies (VIII-DLs); (ii) neutron scattered group-III interstitials are mobile and prone to passivate VIII-DLs, changing the configuration of DLs to monomorphic pure DLs; (iii) after the saturation of the passivation, neutron scattered group-III interstitials begin to escape from the system. The physical analysis is consistent with the trends in the experimental data. Our work provides a new post-processing treatment for reducing the reverse leakage current of AlGaN/GaN heterostructures grown by MOCVD on sapphire substrates. [ABSTRACT FROM AUTHOR]

An 18–56-GHz gallium nitride (GaN) low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) is presented in this letter. This LNA is fabricated with commercial 0.1- $\mu \text{m}$ gate-length GaN-on-silicon (GaN/Si) process. The gain is 16–21.5 dB and the $\vert {S} 11\vert $ and $\vert {S} 22\vert $ are below −5 dB across the band. The noise figure (NF) is 2.2–4.4 dB and the output power at 1-dB compression point (${P} _{\text {1 dB}}$) is 10–20 dBm. This LNA has four-stage-cascade and common-source structure with $4.8\times 1$ mm2 chip area. The dc power dissipation is 1.4 W. To the best of the author’s knowledge, there has been no GaN LNA covering such a wide bandwidth at this frequency range. This LNA shows ultrawide bandwidth, low NF, high linearity, and high robustness. Moreover, it can be directly integrated with GaN power amplifiers (PAs) and switches to realize the monolithic RF front-ends, which can largely reduce the packaging loss and the module volume. This LNA has a great potential in wideband, high-speed, high-reliability, and high-integration applications. [ABSTRACT FROM AUTHOR]

Two low-noise amplifiers fabricated with 100-nm gate length gallium nitride (GaN)-on-silicon process in $W$ -band are presented in this work. One has a gain of 17.5–20.5 dB in 77.5–84 GHz with 3.8–4.7-dB noise figure (NF), the other has wider bandwidth of 78.5–90 GHz with 14.5–17-dB gain and 4.5–5.2-dB NF. The chip sizes of these two low-noise amplifiers (LNAs) are $3\times 1.6$ mm2 and $3\times 1.4$ mm2 separately. The power dissipation of these two LNAs is about 190 mW. These LNAs can be integrated with high-power GaN power amplifier on the same chip, which avoids the peripheral packaging loss and achieves smaller module size. The universal gate length in commercial process with low-cost silicon substrate brings these LNAs great potential for mass production in future millimeter-wave communications. [ABSTRACT FROM AUTHOR]

In this article, a novel design and realization of wideband subharmonic mixer (SHM) operating over the 45‐61 GHz frequency band is presented, in which a dual‐band power divider (DBPD), an antiparallel diode pair (APDP), and a LC low‐pass filter are employed. Working in the two corresponding frequency bands, the DBPD not only imports the RF and the LO signals, but also provides impedance transformation between the APDP, RF, and LO ports. Due to the inherent ports isolation and matching characteristics of DBPD, a simplified and miniaturized configuration of SHM has been achieved. The monolithic microwave integrated circuit (MMIC) is implemented by a GaAs 0.15 μm pHMET process with a compact chip size of 1 × 0.95 mm2 including probe pads. The mixer exhibits 14.8 to 16.5 dB conversion loss with improved return losses at the RF, LO, and IF ports. The LO‐to‐RF, LO‐to‐IF, RF‐to‐IF, 2LO‐to‐RF, and 2LO‐to‐IF isolations are 16.5 to 34.5 dB, 35 to 41.5 dB, 30 to 40 dB, 32.5 to 39.5 dB, and 50 to 61.5 dB, respectively. To the author's best knowledge, the DBPD is used in MMIC SHM design for the first time. [ABSTRACT FROM AUTHOR]

The early stage degradation of electrical properties in AlGaN/GaN high electron mobility transistors (HEMTs) under fast neutron irradiation is studied. After the 1 MeV neutron irradiation at a low fluence of 1 × 1014 neutrons/cm2, the reverse leakage current decreases while the output and transfer characteristics remain unchanged, which cannot be explained by the previously reported high-fluence degradation model. By employing temperature-dependent gate leakage current measurements, we show that the dislocation related Poole–Frenkel (PF) emission dominates the gate leakage mechanism before and after irradiation whereas the barrier height for electron emission to conductive dislocation increases after the neutron irradiation. A model with the evolution of dislocation from the VGa-decorated configuration to the pure configuration is proposed to describe the degradation of AlGaN/GaN HEMTs at the low-fluence early stage neutron irradiation. This model enriches the understanding of the degradation mechanism of neutron irradiated AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]

This paper reports on an in-depth research on the etching-process induced current degradation in AlGaN/GaN heterostructures by experimental research and theoretical calculations. The channel current degrades by 60% after the etching process and recovers to 90% after thermal annealing at 400 °C. It is found that fluorine is incorporated into the heterostructures of both AlGaN and GaN layers during the etching process. The degradation and recovery of the current is accompanied by the change in the concentration of fluorine in both AlGaN and GaN layers during the experiment. First-principles defect calculations of fluorine in GaN indicate that the dominant defect configuration of F is negatively charged interstitial ( F i − ) with the lowest formation energy. The accompanied technology computer-aided design simulation of the energy bands reveals that F i − raises the conduction band minimum of GaN and, thus, decreases the density of the two-dimensional electron gas, causing degradation of the channel current. This result leads to the post-etching recovery treatment without a high temperature process and ohmic contact degradation. [ABSTRACT FROM AUTHOR]

A 23 to 31 GHz low‐noise amplifier (LNA) based on 0.1‐μm gallium nitride (GaN) on silicon (Si) microwave monolithic integrated circuit process is presented in this work. Three‐stage cascade topology was used in the LNA design with chip area of 1.9 × 0.8 mm2. The measured linear gain is 22 to 27 dB with low input and output return loss. The noise figure (NF) was measured with cold source methodology, which is 0.93 to 1.36 dB across the working frequency band. The power characteristics were measured, which indicate that this LNA has 1‐dB compression point output power (P1dB) of 23 dBm and saturated output power (Psat) of 28 dBm. The measured output‐referred third‐order intercept point (OIP3) was at 34 dBm level, which indicates the high linearity of this LNA. To inspect the robustness, 30 dBm continuous wave input power was injected into the working LNA for 5 minutes, no obvious degradation was found after stress. Compared with the traditional gallium arsenide (GaAs) and indium phosphide (InP) LNA, GaN LNA reported in this work has comparable NF but much higher robustness. Moreover, this LNA has very high linearity, which increases the immunity to jamming signal, enables more complicated modulation mode and improves data throughput. As we know, there is no GaN LNA achieving such high P1dB and Psat with NF below 1.4 dB at this frequency band. This GaN LNA has a great potential in the applications of electronic war, anti‐electromagnetic interference and signal detection. [ABSTRACT FROM AUTHOR]

A 23–30-GHz gallium nitride (GaN) low-noise amplifier (LNA) with a noise figure (NF) of 0.87–1.51 dB is presented in this article. This LNA was fabricated with 100-nm gate-length GaN-on-silicon (GaN/Si) microwave monolithic integrated circuit (MMIC) process. The linear gain is 14–17 dB within the band. For investigating the robustness of this LNA, 1-W continuous wave (CW) at 27 GHz was stressed on the input port of the LNA. The gain decreased, and the NF increased after stress. Experimental research and first-principles calculations were carried out to investigate the physical origin of the degradation. The dehydrogenation of VGa-H3 complexes causes the decrease of gain, and the creation of VAl-H4 in the AlN barrier is supposed to cause an increase of NF. [ABSTRACT FROM AUTHOR]

The origin of the threshold voltage (Vth) shift that occurs in ON-state biased AlGaN/GaN high-electron mobility transistors (HEMTs) is proposed in terms of experimental researches and first-principles calculations. Experimentally, ∼20% negative shift of the Vth is found for the 0.2 μm gate length T-gate AlGaN/GaN HEMT under the ON-state stress. 1/f noise measurements are carried out to investigate the evolution of defect distribution in the GaN channel, which indicates that the Vth shift is accompanied by the diminishing of the defect level of Ev + 0.8 eV. Combined with first-principles studies based on hybrid functionals defect calculations, we find that the defect evolution of O from negatively charged VGa-ON to neutral ON-H gives rise to the decrease in acceptors in the GaN channel and thus the negative shift of Vth. Our work indicates that the strengthening of oxygen-related defects in GaN during material growth and device fabrication would improve the reliability of AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]

A 23.5‐30 GHz power amplifier (PA) using 0.1‐μm gallium nitride (GaN) on silicon (Si) microwave monolithic integrated circuit (MMIC) process is presented in this work. The area of this PA MMIC is 3.7 mm × 3.2 mm (11.8 mm2). The measured linear gain is 16.4‐19.4 dB with input/output return loss over 10 dB. The measured saturation output power (Psat) is 7.6‐12.4 W under pulsed working condition. The drain voltage is 12 V and the total drain current is 2.6 A, which induce a power added efficiency (PAE) of 26%‐37%. The reported GaN on Si (GaN/Si) PA has high power, high efficiency and low cost. It is more suitable for massive commercial application compared with the traditional GaN on silicon‐carbon (GaN/SiC) PA. As we know, there has been no high output power GaN/Si PA as high as 10 W level reported in the 20‐30 GHz frequency region. [ABSTRACT FROM AUTHOR]

Abstract: GaN technology has attracted main attention towards its application to high‐power amplifier. Most recently, noise performance of GaN device has also won acceptance. Compared with GaAs low noise amplifier (LNA), GaN LNA has a unique superiority on power handling. In this work, we report a wideband Silicon‐substrate GaN MMIC LNA operating in 18‐31 GHz frequency range using a commercial 0.1 μm T‐Gate high electron mobility transistor process (OMMIC D01GH). The GaN MMIC LNA has an average noise figure of 1.43 dB over the band and a minimum value of 1.27 dB at 23.2 GHz, which can compete with GaAs and InP MMIC LNA. The small‐signal gain is between 22 and 25 dB across the band, the input and output return losses of the MMIC are less than −10 dB. The P1dB and OIP3 are at 17 dBm and 28 dBm level. The four‐stage MMIC is 2.3 × 1.0 mm2 in area and consumes 280 mW DC power. Compared with GaAs and InP LNA, the GaN MMIC LNA in this work exhibits a comparative noise figure with higher linearity and power handling ability. [ABSTRACT FROM AUTHOR]

A 22–30-GHz gallium nitride (GaN) low-noise amplifier (LNA) having a noise figure (NF) of 0.4–1.1 dB is presented in this letter. This LNA is fabricated with 0.1 gate-length GaN-on-silicon high-electron mobility transistor process, which is believed to have the lowest NF among GaN LNA at this frequency range reported to date. The small-signal gain is between 19.5 and 22.5 dB across the band. The output-referred 1-dB compression point (P1dB) and output-referred third-order intercept point (OIP3) are at 20.8- and 34.5-dBm level. The high robust was proven by stressing the LNA with a continuous wave input power of 30 dBm for 1 min. The three-stage LNA is $1.7\times1.3$ mm2 in area and consumes 210-mW dc power. Compared with the traditional gallium arsenide and indium phosphide LNA, the GaN monolithic microwave integrated circuit LNA in this letter exhibits a competitive NF but has much higher robust and linearity. [ABSTRACT FROM AUTHOR]

ABSTRACT In this letter, Ti/Pt/Au metal system has been investigated for the source/drain contact of MHEMT, the Ti/Pt/Au contact exhibits good ohmic contact characteristics with well thermal stability in the temperature range from 280 to 340°C. To further optimize the contact resistance, different metal deposition methods and contact layers are experimentally investigated. With sputtering Pd as an interlayer between Ti/Pt/Au and n+-InGaAs, the specific contact resistivity is further reduced to 3.51 × 10−5 Ω cm2. Meanwhile, by adopting this metal contact system, the MHEMT shows good DC and RF characteristics, including full channel current of 75 mA/mm, extrinsic maximum transconductance gm.max of 96 ms/mm, unity current gain cutoff frequency fT of 60 GHz and maximum frequency of oscillation fmax of 156 GHz. These good electrical characteristics demonstrate that this metal contact system is beneficial for the performance improvement of MHEMT. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:217-221, 2016 [ABSTRACT FROM AUTHOR]

Objective: To develop an immunomagnetic cell separation system for allogeneic hematopoietic stem cell (HSC) transplantations, which can achieve a high level of T-cell depletion (at least 4.0 log10), high level of recovery of hematopoietic stem cells (>90%), with a high throughput (>106 cells/second). Methods: Peripheral blood leukocytes (PBLs) from buffy coats were spiked with CD34-expressing cells (KG1a) to mimic a leukaphoresis product containing stimulated HSCs. T cells were labeled with anti-CD3+ Dynabeads and separated in a quadrupole magnetic cell sorter (QMS). The performance of the system with respect to T-cell depletion and recovery of non–T cells and spiked KG1a was determined using four-color, flow cytometry analysis, with the aid of Trucount cell-concentration calibration beads. Limiting dilution assays were also performed to quantify the log10 depletion of clonable T cells. Results: While the general performance of the QMS system is governed by proven theoretical principles, significant system variability exist, not all of which can be explained by our current understanding. Consequently, a factorial design was employed, guided by JMP software, to optimize the labeling conditions and operation of the QMS focused on maximizing the depletion of T cell, and recovery of unlabeled cells including KG1a cells. From these studies, an optimized, no wash, immunomagnetic labeling protocol and optimized QMS operating conditions were developed. For an average initial cell concentration of 1.7 × 108 total cells, an average 3.96 ± 0.33 log10 depletion (range, 3.53–4.34) of CD3+CD45+ cells with a mean 99.43% ± 4.23% recovery of CD34+CD45+ cells (range, 94.38–104.90%) was achieved at a sorting speed of 106 cells/s (n = 6). Limiting dilution assays on the T-cell depleted fractions, which gave a log10 depletion of 3.51 for the clonable T cells. Conclusion: We suggest that this system will provide superior performance with respect to T-cell depletion and CD34+ recovery for clinical allogeneic bone marrow transplants. Ongoing studies, on a clinical scale, are being conducted to demonstrate this claim. [Copyright &y& Elsevier]

To develop a reliable technique to enrich for rare cells in blood suspensions using only negative selection steps including a flow-through immunomagnetic cell separations system and by optimizing variables normally encountered during such enrichment processes.A human breast cancer cell line was cultivated and spiked at a ratio of 1 cancer cell to 105 total leukocytes in buffy coat or 1 cancer cell to 108 total cells in whole blood samples. The final, optimized process consisted of: a red cell lysis step, immunomagnetically staining leukocytes with an anti-CD45 PE, anti- MACS sandwich, immunomagnetic sorting using a flow-through system (QMS), and a final cell analysis step using either an automated cell counter, filtration, and visual counting or a cytospin analysis.The final, optimized process produced a final enrichment of the rare cancer cells of 5.17 log10 and an average, final recovery of 46%. It should be noted that a negative depletion protocol was used (i.e., no labeling of the rare cancer cells was used).To the authors'' knowledge, no examples in the literature exist of a 5.17 log10 enrichment of cancer cells in human blood using a negative depletion protocol. The closest example is a 4 log10 enrichment in which two positive magnetic cell separation steps were used (none were used in this study). Ongoing studies are investigating further modifications of the precommercial, prototype flow-through immunmagnetic separation system to increase both the enrichment and recovery rate. However, even at current performance levels, the presented process could significantly improve visual and molecular analysis of rare cells in blood. [Copyright &y& Elsevier]

This work studied the regulation of hole concentration and mobility in p-InGaN layers grown by metalorganic chemical vapor deposition (MOCVD) under an N-rich environment. By adjusting the growth temperature, the hole concentration can be controlled between 6 × 1017/cm3 and 3 × 1019/cm3 with adjustable hole mobility from 3 to 16 cm2/V.s. These p-InGaN layers can meet different requirements of devices for hole concentration and mobility. First-principles defect calculations indicate that the p-type doping of InGaN at the N-rich limiting condition mainly originated from Mg substituting In (MgIn). In contrast with the compensation of nitrogen vacancy in p-type InGaN grown in a Ga-rich environment, the holes in p-type InGaN grown in an N-rich environment were mainly compensated by interstitial Mg (Mgi), which has very low formation energy. [ABSTRACT FROM AUTHOR]

This letter presents a modified Gysel power divider for dual-band applications. A short-stub and an open-stub has been attached to the conventional Gysel structure. Closed-form design equations are derived. Power operation analysis shows that the new dual-band circuit maintains Gysel divider's high power handling advantage over Wilkinson divider. The measured results show that good matching, isolation and power transmission can be achieved at two operating frequency bands. [ABSTRACT FROM PUBLISHER]

Detection of rare, circulating tumor cells (CTC's) in human peripheral blood is a potential indicator of prognosis and diagnosis in oncology. Typical methods to detect these CTC's are either by immunocytochemistry (ICCS) or RT-PCR. However without accurate, rapid, and reproducible enrichment processes, these detection techniques are labor intensive and/or unreliable. In this article, a repeatable enrichment process that included a flow-through immunomagnetic cell separation system, the quadrupole magnetic sorter (QMS) was optimized with the aid of a statistical analysis software package. The QMS was operated in a negative mode of operation by immunomagnetically targeting normal human peripheral blood lymphocytes (PBL) through the CD45 surface marker. Three head and neck squamous carcinoma cell lines (HNSCC), Detroit-562, SCC-4, and CAL-27, were used to determine the sensitivity of RT-PCR for the epidermal growth factor receptor (EGFR) in spiked PBL. The detection purity needed for detection was found to be one cell in 10(4), one cell in 10(3), and one cell in 10(5) for the Detroit-562, SCC-4, and CAL-27, respectively. The actual number of cancer cells needed for RT-PCR detection ranged from 30 to 1 cell. To mimic the potential concentration of rare CTC present in peripheral blood of cancer patients, the spiking concentration was chosen to be one cancer cell per 10(5) total leukocytes from healthy donors. Using a single step immunomagnetic labeling, the final, optimized enrichment process produced a 57.6 +/- 30.3-fold (n = 6) enrichment of the rare cancer cells with a final cancer cell recovery of (77.8 +/- 6.6)%., (Copyright 2007 Clinical Cytometry Society.)