Ho-Kyun Ahn

Single supply, high linearity, high efficient PHEMT power devices and amplifier for 2 GHz & 5 GHz WLAN applications

A single supply, high linearity, high efficient power devices and amplifier MMIC is implemented utilizing high performance of quasi-enhanced power PHEMT technology. The PHEMT power device features Vth= ¿0.65 V, Vbdg=26 V, Imax=144 mA/mm at Vgs=0.2 V, Gm=340 mS/mm. When matched on-wafer compromise between power and efficiency, the OIP3 at peak IP3 is 40.5 dBm for 2 GHz and 37.0 dBm for 5.8 GHz, respectively. The power amplifier achieves at 5.8 GHz Pout=27 dBm with associated PAE=45% at 5 V under Vgs=0 V, GL=14.5 dB, OIP3=37.5 dBm.

Experimental Study on Isolation Characteristics Between Adjacent Microstrip Lines Employing Periodically Perforated Ground Metal for Application to Highly Integrated GaAs MMICs

Using a periodically perforated ground metal (PPGM) on GaAs monolithic microwave integrated circuit (MMIC), a microstrip line structure with a high isolation characteristic between lines was developed. The high isolation characteristic was originated from a resonance between adjacent microstrip lines employing PPGM. According to experimental results, a much better isolation characteristic was observed from the adjacent microstrip lines employing PPGM compared with conventional microstrip lines, and the frequency range for high isolation was easily controlled by changing the PPGM structure. Above results indicate that microstrip lines employing PPGM are very useful for application to compact signal/bias lines of highly integrated MMIC requiring a high isolation characteristics between lines.

Microwave Low-Noise Performance of

Microwave low-noise performance AlGaN/GaN HEMT on a SiC substrate with a wide head double-deck T-shaped gate has been reported. The HEMTs with gatelength (L_g) of 0.17 μm and source-drain spacing (L_sd) of 3.5 μm exhibited a maximum extrinsic transconductance of 360 mS/mm, a current gain cutoff frequency (f_T) of 50 GHz, a maximum oscillation frequency (f_max) of 149 GHz, and three-terminal breakdown voltage of 113 V. The device exhibited a minimum noise figure (NF_min) of 0.50 and 0.84 dB at 10 and 18 GHz, respectively, when biased at V_ds = 5 V and I_ds = 140 mA/mm, which is the lowest noise characteristics ever reported for the GaN-based T-shaped gate HEMTs with gate length larger than 0.1 μm. This excellent noise performance is attributed to the reduction of the gate resistance resulting from a wide head T-shaped gate and the improved device characteristics.

0.17~\mu \text{m}

We report the fabrication of a 0.12 µm T-gate with a silicon nitride assisted process. A two-step etch process was performed to define the gate footprint in the SiNx. The SiNx was etched either by dry etching (RIE) alone or by using a combination of wet and dry etching. The gate recessing was done in two steps including a wet etching for the removal of the damaged surface layer and a dry etching for the narrow recess. We have seen that the increases of the cut-off frequency fT and the maximum oscillation frequency fmax are 39% and 16%, respectively. This was believed to be due to a remarkable decrease of the gate-source and gate-drain capacitances by 25% and 18.3%, respectively. The improvement in RF performance can be understood in terms of the decrease in parasitic capacitances due to SiNx and the gate recess etching method.

Gate-Length AlGaN/GaN HEMTs on SiC With Wide Head Double-Deck T-Shaped Gate

A plasma-enhanced chemical vapor deposited (PECVD) silicon–nitride-assisted process has been used to fabricate 0.12 µm T-shaped AlGaAs/InGaAs/GaAs PHEMTs. A two-step SiNx etch was performed to define the T-gate footprint. The SiNx was etched either by dry etching alone or using a combination of wet and dry etching. A structure for the top of the T-gate which consists of a wide head part and a narrow lower layer part has been employed, taking advantage of the large cross-sectional area of the gate and its mechanically stable structure. The gate recessing was carried out in two steps including a wet etching for removal of the damaged surface layer and a dry etching for the narrow recess. The cut-off frequency of the device fabricated by the two-step etch process is higher than that of the device fabricated by dry etching alone. We have observed the increase of the cut-off frequency fT and the maximum oscillation frequency fmax, by 39% and 16%, respectively. This is believed to be due to considerable decreases of the gate–source and gate–drain capacitances, by 25% and 18.3%, respectively. This improvement in RF performance can be understood in terms of the decrease in parasitic capacitances which is due to the use of the dielectric and the gate recess etching method. The minimum noise figure is 1.6 dB, with a 6.9 dB associated gain at 39 GHz.

Fabrication and characteristics of 0.12 µm AlGaAs/InGaAs/GaAs pseudomorphic HEMT using a silicon nitride assisted process

Surface passivation of AlGaN/GaN heterojunction structure was examined through the thermal oxidation of evaporated Al. The Al-oxide passivation increased channel conductance of two dimensional electron gas (2DEG) on the AlGaN/GaN interface. The sheet resistance of 463 ohm/ for 2DEG channel before passivation was decreased to 417 ohm/ after passivation. The oxidation of Al induces tensile stress to the AlGaN/GaN structure and the stress seemed to enhance the sheet carrier density of the 2DEG channel. In addition, the films formed by thermal oxidation of Al suppressed thermal deterioration by the high temperature annealing.

0.12 µm Gate Length T-Shaped AlGaAs/InGaAs/GaAs Pseudomorphic High-Electron-Mobility Transistors Fabricated Using a Plasma-Enhanced Chemical Vapor Deposited Silicon–Nitride-Assisted Process

In this paper, the fabrication technology of SiN- assisted 0.12 um double deck T-gate AlGaAs/InGaAs p-HEMT and 60 GHz-band MMICs for high rate personal area network (WPAN) systems is described. The effect of the gate head dimension, such as the 1st-deck and the 2nd-deck gate head size, on the DC and RF characteristics of the p-HEMT device and the device performance at the optimum gate head size are also presented. At the optimum gate head size, the p-HEMT device with two finger gates of 0.12 um length and 50 um width showed an extrinsic transconductance of 511 mS/mm and a drain current of 20.6 mA at 1.5 V of drain voltage. The cut-off frequency and the maximum frequency of oscillation were 96.8 GHz and 192.6 GHz, respectively. Gate head dimensions of the p-HEMT device are correlated to parasitic capacitances, including Cgs, which effect the RF performance including a cut-off frequency (fT) and a maximum frequency of oscillation (fmax).

Effect of Al 2 O 3 Surface Passivation by Thermal Oxidation of Aluminum for AlGaN/GaN Structure

In this work, using theoretical and experimental analysis, basic characteristics of the microstrip line employing PPGM (periodically perforated ground metal) was investigated in order to evaluate its suitability for application to a development of miniaturized on-chip passive components. According to the results, it was found that the PPGM structure is a promising candidate for application to a development of miniaturized components on MMIC (monolithic microwave integrated circuit). In addition, basic characteristics of the coupled microstrip line employing PPGM was also investigated. Theoretical and experimental investigation indicated that microstrip lines employing PPGM are very useful for application to compact signal lines of highly integrated MMIC requiring a high isolation characteristics between lines.

Influence of Gate Head Dimensions on the Device performance of 0.12um PHEMT

A narrow-band preamplifier for fiber-optic millimeter-wave wireless system is presented based on a fully stabilized 0.12 mum pseudomorphic high electron mobility transistor (PHEMT) technology and is realized in a low-temperature co-fired (LTCC) technology. The preamplifier is designed with parallel feedback and T-section matching networks. These networks are used for narrow-band filtering function and for unconditionally stable of circuits. The preamplifier module, in corporation of four amplifying stages, shows measured transimpedance gain of 53 dBOmega, and return loss of less than -10 dB with a 1 dBOmega, ripple around the center frequency. The transimpedance gain difference between bare chip and module is about 3.5 dBOmega

Basic RF Characteristics of the Microstrip Line Employing Periodically Perforated Ground Metal on MMIC

We report the fabrication and DC and microwave characteristics of 0.12 µm double-recessed T-gate AlGaAs/InGaAs/GaAs pseudomorphic high-electron-mobility transistors (PHEMTs) using dielectric-assisted process. Silicon nitride layers 300 and 200 A thick were deposited by plasma-enhanced chemical vapor deposition (PECVD) at 260 °C to protect the device and to define the gate footprint. The double-recess process was carried out by two different etching techniques to obtain double-recessed T-gates with 0.12 µm gate lengths. Completed double-recessed T-gate AlGaAs/InGaAs/GaAs pHEMT devices fabricated using dry etching exhibited a peak transconductance, gm, of 765 mS/mm, a current-gain cutoff frequency ( fT) as high as 124 GHz, and a maximum oscillation frequency ( fmax) of 247 GHz. The fabricated low-noise amplifier (LNA) has a measured gain of more than 20 dB in the 62.75 to 64.75 GHz frequency range.