Hsien-Chin Chiu

Low Hysteresis Dispersion La2O3 AlGaN ∕ GaN MOS-HEMTs

AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using electron-beam evaporated high-dielectric-constant (high-k) lanthanum oxide layer (La 2 O 3 ) as the gate insulator have been investigated and compared with the traditional GaN HEMTs. The dielectric constant of the La 2 O 3 insulator layer developed in this study was 13.1. In addition, a negligible hysteresis voltage shift in the capacitance-voltage curves can be obtained after high temperature annealing. The compositions and the crystalline structures of La 2 O 3 with different annealing temperatures were observed by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The La 2 O 3 thin film achieved a good thermal stability after 200, 400, and 600°C postdeposition annealing owing to its high binding energy (835.7 eV) characteristics. Moreover, the gate leakage current of a traditional metal gate GaN HEMT can be suppressed for 1 order of magnitude after inserting a La 2 O 3 insulator between Ni and AlGaN, resulting in a better pulsed-mode operation. The device linearity was also improved due to its flat and wide transconductance (g m ) distribution, which was analyzed by a polynomial curve-fitting technique. Therefore, La 2 O 3 is a potential candidate high-k material for the gate insulator to enhance the GaN-based field effect transistor performance while scaling down the device dimension and device reliability at high power operation.

Improved device linearity of AlGaAs/InGaAs HFETs by a second mesa etching

The conventional mesa isolation process in AlGaAs/InGaAs heterostructure FETs results in the gate contacting the exposed highly doped region at the mesa sidewalls, forming a parasitic gate leakage path. In this work, we suppress the gate leakage from the mesa-sidewall and enhance microwave power performance by performing an additional second mesa etching. The device gate leakage characteristics under high-input power swing are particularly investigated to reveal an improvement in device linearity, which is sensitive to the sidewall gate leakage. This modified device (M-HFETs) provides not only a higher linear RF output power but also a lower IM3 product than those characteristics in conventional HFETs.

28-GHz patch antenna arrays with PCB and LTCC substrates

Ka-band spectrum is relatively abundant and therefore attractive for services of satellite communication, targeting radar, and wireless broadband access technologies. However, Ka-band patch antenna is difficult in realization because the accurate manufacturing is indeed a challenge in obtaining excellent antenna performance at such high frequencies. This study develops three patch antenna arrays for operation at 28 GHz. Two of the three patch arrays with 2×2 and 4×1 patches, respectively, are realized on microwave printed circuit boards (PCBs). The experimental PCB patch arrays have bandwidths up to 5.7% and gains up to 13 dBi. Another 2×2 stacked-patch antenna array is fabricated with low temperature co-fired ceramic (LTCC) technology for further bandwidth enhancement. This LTCC stacked-patch array comprises a novel opposite-side feeding structure to prevent any electrical effect on the parasitic patch. A measured gain of 10.35 dBi and a wide bandwidth of 10.1% (26.75–29.6 GHz) are achieved.

Device Characteristics of AlGaN/GaN MOS-HEMTs Using High-

In this brief, AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) using an electron-beam-evaporated praseodymium oxide layer (Pr₂O₃) in a high-oxygen-flow environment during the gate-dielectric-layer formation was studied. By adjusting the oxygen flow rate in an electron-beam evaporator chamber, the highest Pr content in Pr₂O₃ occurred at 15 sccm. Moreover, the Pr₂O₃ thin film also achieved a good thermal stability after 400-degC, 600-degC, and 800-degC postdeposition annealing due to its high-binding-energy (933.2 eV) characteristics. The gate leakage current can be improved significantly by inserting this high- <i>k</i> dielectric layer, and meanwhile, the power-added efficiency can be enhanced up to 5%. Experimental results have also shown that Pr₂O₃ MOS-HEMTs outperformed the standard GaN HEMTs in output power density and in pulsed-mode operation. These high-performance electron-beam-evaporated Pr₂O₃ high-<i>k</i> AlGaN/GaN MOS-HEMTs are suitable for high-volume production due to its <i>in</i> <i>situ</i> insulator and metal-gate deposition in the same chamber.

k

An ultra-wideband CMOS voltage-controlled oscillator (VCO) with 3-5 GHz tuning range is presented in this paper. The circuit was designed and fabricated by using TSMC 0.18-/spl mu/m CMOS process. The proposed VCO is using the tunable active inductor to replace the passive spiral inductor. The active inductor can vary the inductance between 1.5/spl sim/7 nH with quality-factor > 30 by a feedback tunable resistor. Comparisons of this topology with conventional VCO show that this topology achieves better performance with very wide tuning range and compact chip size. The tuning range is approximately from 3 to 5 GHz for ultra-wideband system applications.

Praseodymium Oxide Layer

This paper elucidates the dc, pulse I-V , microwave, flicker noise, and power properties of AlGaAs/InGaAs pseudo- morphic high electron mobility transistors (pHEMTs) after var- ious ex situ sulfur pretreatments. The pHEMTs were pretreated with NH4 OH, (NH4 )2 SX ,a nd P 2 S5 /(NH4 )2 SX solutions before SiO2 passivation to reduce the GaAs native oxide-related surface states. Stable phosphorus oxides and sulfur bound to the Ga and As species can be efficiently obtained using P2 S5 /(NH4 )2 SX pre- treatment; therefore, the leakage current in pHEMT was reduced following this process. Atomic force microscopy measurements in- dicated that the phosphorus oxides formed by P2 S5 /(NH4 )2 SX treatment also provided a better surface roughness than obtained following traditional (NH4 )2 SX-only pretreatment, reducing mo- bility degradation after sulfur pretreatment. Based on the dc and 1 µs pulse I-V measurement results, P2 S5 /(NH4 )2 SX-treated pHEMT exhibited very similar Ids trends, especially at high cur- rents; however, NH4 OH, (NH4 )2 SX treatments clearly reduced the current upon pulse measurement because of the presence of surface traps. Hence, this novel pretreatment method has great potential for highly linear microwave power transistor applications. Index Terms—Linearity, passivation, pseudomorphic high elec- tron mobility transistor (pHEMT), power, sulfur.

An ultra-wideband CMOS VCO with 3-5 GHz tuning range

This study presents a Ku-band band-pass filter designed and fabricated with a commercial CMOS technology. The filter utilizes a pi-network coupling structure to construct the desired coupling and the resonant tanks on Si substrate with a compact size and the low-loss performance. A method of synthesizing pi-network filter is proposed. A 17GHz filter chip was fabricated by 0.18mum CMOS technology. The size of filter is 0.56mmtimes0.6mm and the measured pass-band insertion loss of filter is about 3.2dB

Electrical Characteristics of Passivated Pseudomorphic HEMTs With

In this letter, enhancement-mode AlGaN/GaN metal-oxide semiconductor high-electron-mobility transistors (HEMT) (MOS-HEMTs) are realized by using N₂O plasma oxidation and Gd₂O₃ stacked-gate dielectric technologies. Before the gate metal was deposited, the AlGaN barrier layer was treated by 150-W N₂O plasma for 200 s to remove the AlGaN native oxide layer and, simultaneously, to form Al₂O₃/ Ga₂O₃ compound insulator. Then, a 10-nm-thick high-dielectric-constant Gd₂O₃ thin film was electron-beam evaporated as a stacked-gate dielectric. To elucidate the interface phenomena of the device, the dependence of the 1/<i>f</i> noise spectra on the gate bias was studied. The fluctuation that is caused by trapping/detrapping of free channel carriers near the gate interface can be reduced by N₂O plasma treatment. Additionally, the variation of the Hooge factor (α<i>H</i>) of a traditional metal gate GaN HEMT, measured at 77 K and 300 K, is huge, particularly in the subthreshold gate voltage regime. The tunneling leakage current that is induced by the interface traps is determined to be higher than that in the MOS-HEMT design. The threshold voltage (<i>V</i>_th) of depletion-mode GaN HEMT was -3.15 V, and this value can be shifted to +0.6 using N₂O-treated stacked-gate AlGaN/GaN MOS-HEMTs.

\hbox{P}_{\hbox{2}}\hbox{S}_{\hbox{5}}/(\hbox{NH}_{\hbox{4}})_{\hbox{2}}\hbox{S}_{\hbox{X}}

GaAs-based pseudomorphic high electron mobility transistors (pHEMTs) in which the field-plate (FP) is connected to the gate terminal and the source terminal, were developed and evaluated experimentally to determine their microwave and power performance. The small gate-to-drain feedback capacitance (Cgd) and the stable FP-induced depletion region at high input power (Pin) of the source-terminated FP pHEMT (FP-S pHEMT) greatly improve the power and linearity of the FP-S pHEMT above those of the gate-terminated FP pHEMT (FP-G pHEMT). The power ratio of the fundamental to the third-order inter-modulation product (IM3) is 18.8 dBc for FP-S pHEMT for Pin = 0 dBm; the corresponding value for FP-G pHEMT is 12.4 dBc. These experimental results indicate that the FP architecture is more effective at high-power operation and exhibits high linearity in high-power pHEMT applications.

Pretreatment

High-power and high-efficiency GaAs heterostructure field-effect transistors (FETs) are attracting tremendous attention in RF power amplifier applications. However, thermal effects can be an important issue in RF power devices, owing to the huge amount of heat generated during their operation. In this paper, the temperature-dependent characteristics of Al/sub 0.3/Ga/sub 0.7/As/In/sub 0.15/Ga/sub 0.85/ As doped-channel FETs (DCFETs) are investigated and compared with conventional pseudomorphic-HEMTs (pHEMTs) devices, in terms of their dc, microwave and RF power performance at temperatures ranging from room temperature to 150/spl deg/C. Due to conducting carriers being less influenced by temperature and the better Schottky diode characteristics that can be obtained in DCFETs, the intrinsic device parameters and output performance remain almost constant at high temperatures, which also results in better device reliability. The performance variation of DCFETs associated with temperatures from 25/spl deg/C to 150/spl deg/C all fall within a single digit, i.e., output power (P/sub out/, 16.2 dBm versus 15.8 dBm), power gain (G/sub p/, 16.6 dB versus 15.1 dB), power added efficiency (PAE, 34.2% versus 31.3%), which is not the case for conventional pHEMTs. Therefore, DC devices are very promising for microwave power device applications operating at high temperature.