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A new slotted ground structure featuring compact size and spurious-free passband in the context of microstrip lines is proposed. The compactness of the new structure originates from the lengthened coupling gap in the ground. The spurious-free response in a wide passband is a result of combining both narrow and wide slots in the new structure, which effectively forms a stepped-impedance slot resonator. Compared to the previously proposed dumbbell- and H-shaped defected ground structure, over 40% size reduction can be realized in the new structure. The new structure also provides flexibilities in introducing additional functionalities to the bandstop resonators. By embedding varactors in the slotted ground structure, tunable bandstop resonators can be implemented and 13% tuning range centered at 2.36 or 2.67 GHz have been obtained. Index Terms--Defected ground structure, microstrip, slotted ground structure, tunable bandstop resonator.

A low phase-noise X-band monolithic-microwave integrated-circuit voltage-controlled oscillator (VCO) based on a novel high-linearity and low-noise composite-channel [Al.sub.0.3][Ga.sub.0.7]N/[Al.sub.0.05][Ga.sub.0.95]N/GaN high electron mobility transistor (HEMT) is presented. The HEMT has a 1 [micro]m x 100 [micro]m gate. A planar inter-digitated metal-semiconductor-metal varactor is used to tune the VCO's frequency. The polyimide dielectric layer is inserted between a metal and GaN buffer to improve the Q factor of spiral inductors. The VCO exhibits a frequency tuning range from 9.11 to 9.55 GHz with the varactor's voltage from 4 to 6 V, an average output power of 3.3 dBm, and an average efficiency of 7% at a gate bias of -3 V and a drain bias of 5 V. The measured phase noise is -82 dBc/Hz and -110 dBc/Hz at offsets of 100 kHz and 1 MHz at a varactor's voltage ([V.sub.tune]) = 5 V. The phase noise is the lowest reported thus far in VCOs made of GaN-based HEMTs. In addition, the VCO also exhibits the minimum second harmonic suppression of 47 dBc. The chip size is 1.2 x 1.05 [mm.sup.2]. Index Terms--[Al.sub.0.3] [G.sub.0.7]N/[Al.sub.0.05][Ga.sub.0.95]N/GaN high electron mobility transistor (HEMT), monolithic, phase noise, voltage-controlled oscillator (VCO).

The dc and radio-frequency (rf) characteristics of [Al.sub.0.3][Ga.sub.0.7]N/GaN/[In.sub.0.1][Ga.sub.0.9]N/GaN double-heterojunction HEMT (DH-HEMT) structure are analyzed. The E-mode devices with good dc, RF small signal, and power performances are fabricated on the InGaN-notch DH-HEMT structure by using C[F.sub.4] plasma treatment before the deposition of the gate electrodes.

A physical-based analytical model for on-chip spiral inductors with accurate substrate modeling is developed. This generic model can be applied to various substrate resistivities and can also facilitate the design and optimization of on-chip inductor for radio-frequency (RF) IC applications.

The monolithic integration of enhancement/depletion-mode (E/D-mode) HEMTs in the GaN material system is demonstrated based on a novel technique of fabricating high-performance E-mode HEMT using fluoride-based C[F.sub.4] plasma treatment. The integration technology, used to fabricate integrated AlGaN/GaN HEMT inverters and ring oscillators for evaluating the performance of the digital IC technology, results in an improved input voltage swing by about 1V for the E-mode HEMT.

A fabrication method with an accurate control of threshold voltages ([V.sub.th] of AlGaN/GaN high-electron mobility transistors (HEMTs) using a fluoride-based plasma treatment is presented, whereby the [V.sub.th] of AlGaN/GaN HEMTs can be continuously shifted from -4V in a conventional depletion-mode HEMT to 0.9V in an enhancement-mode HEMT. A physical model of the threshold voltage is provided to analyze the effects of the fluoride-based plasma treatment on AlGaN/GaN HEMTs.

The samples grown on a low-cost silicon substrate fabrication process were used to demonstrate the high-performance enhancement-mode AlGaN/GaN HEMTs (E-HEMTs) based on a fluoride-based plasma treatment of the gate region and postgate annealing at 450 degree Celsius. It was found that the fabricated HEMTs almost had the same peak transconductance and cutoff frequencies as the depletion-mode HEMTs and suggested little mobility degradation by plasma treatment.

In this paper, a compact computer-aided design (CAD)-oriented frequency-independent equivalent-circuit model, taking the skin effect, proximity effect, and substrate effect into consideration, is presented for the edge-suspended coplanar waveguide (ESCPW) on lossy silicon substrate. The ESCPWs exhibit the benefit of reduced loss, while avoid the reliability issues that are associated with the suspended coplanar waveguides. The model shows good agreement with the measured insertion loss and the extracted RLGC line parameters up to 25 GHz. With the model, the relationship between physical perimeters of the ESCPWs and the electrical characteristics is also investigated. Moreover, cross-coupling between adjacent ESCPWs with common ground is characterized and modeled. Index Terms--Cross-coupling, edge-suspended coplanar waveguide (ESCPW), equivalent-circuit model, inductively coupled plasma deep reactive ion etching (ICP-DRIE), micromachining.

We report several types of coplanar waveguide tri-section stepped-impedance resonator (SIR) structures that offer further size reduction compared to the conventional two-section SIRs. In addition, the tri-section SIRs provide flexibility of introducing effective capacitive coupling to the ground lines for realizing slow-wave structures. The slow-wave effect can be used to implement more compact bandpass filters. The principles of achieving size reductions using tri-section SIRs are described and confirmed by simulation results. To demonstrate the effectiveness of the proposed tri-section SIRs in size reduction, the tri-section SIRs with slow-wave effects were implemented in a two-pole directly coupled bandpass filter and a fourth-order quasi-elliptic bandpass filter with reduced size. The measured results matched well with the theoretical prediction. Index Terms--Bandpass filters, cascaded quadruplet (CQ) filter, coplanar waveguide (CPW), fractional bandwidth (FBW), stepped-impedance resonator (SIR).

In this paper, we present the detailed fabrication process, high-frequency characterization, and modeling of through-wafer copper-filled vias ranging from 50- to 70-[micro]m-in diameter on 400-[micro]m-thick silicon substrates. The high aspect ratio via-holes were fabricated by carefully optimizing the inductively coupled plasma deep reactive ion etching process. The high aspect ratio via-holes are completely filled with copper using a bottom-up electroplating approach. The fabricated vias were characterized using different resonating structures based on which the inductance and resistance of the filled via-holes are extracted. For a single 70-[micro]m via, the inductance and resistance are measured to be 254 pH and 0.1 [ohms], respectively. In addition, the effect of the physical arrangement and distribution in multiple-via configurations on the resulting inductance is also evaluated with double straightly aligned quadruple and diagonally aligned quadruple vias. Physical mechanisms of the dependence was depicted by electromagnetic simulation. An equivalent-circuit model is proposed and model parameters are extracted to provide good agreement. Index Terms--Microelectromechanical systems (MEMS), RF packaging, silicon substrate, through-wafer interconnects (TWIs), via-holes.

The design, fabrication and characterization of AlGaN-GaN double-channel of high-electron mobility transistors (HEMTs) are presented. Two carrier channels are formed in an AlGaN-GaN-AlGaN-GaN multilayer structure grown on a sapphire substrate.

A high performance InP-based enhancement-mode high electron mobility transistor (E-HEMT) fabrication involves the use of non-alloyed ohmic contacts and Pt-based buried gate technologies. The technique lowers the source resistance. An E-HEMT with a 0.5 micrometer gate shows a minimum transconductance of 1170 millisecond/millimeter. The fabrication procedure involves making depletion-mode HEMT's first and then later annealing them at 250 degrees celsius to give E-HEMT's. The process maintains the source resistance at about 0.2 ohm-millimeters.