Yu-Chi Yang

Performance Improvement in RF LDMOS Transistors Using Wider Drain Contact

In this letter, we proposed a new layout structure for RF laterally diffused metal-oxide-semiconductor (LDMOS) transistors. In a multifinger layout, the drain contact region was designed to be wider than the channel region. The wider drain increases the equivalent drift region width to reduce the drift resistance and suppress the quasi-saturation effect. We found that the wide-drain multifinger LDMOS devices have lower on-resistance, higher cutoff frequency, higher maximum oscillation frequency, and better power performances than the standard multifinger ones.

Characterization of annular-structure RF LDMOS transistors using polyharmonic distortion model

An annular-structure lateral-diffused metal-oxide semiconductor (LDMOS) RF transistor with polyharmonic distortion (PHD) model characterized by nonlinear vector network analyzer is described in this paper. The devices were fabricated using a 0.5 µm LDMOS process. The DC, small-signal, and large-signal characteristics of RF LDMOS transistors with annular-structures were also studied in this work. Using the PHD model, the accuracy of intermodulation and time waveform is verified. Furthermore, the model via X-parameter shows good agreement without optimization.

Characterization of RF Lateral-Diffused Metal–Oxide–Semiconductor Field-Effect Transistors with Different Layout Structures

The DC and RF characteristics of lateral-diffused metal–oxide–semiconductor (LDMOS) transistors with different layout structures were studied. The devices were fabricated using a 0.5 µm LDMOS process. The ring and fishbone structures, which are used widely in power devices, were designed and analyzed. We found that the transconductance, on-resistance, cutoff frequency and maximum oscillation frequency were improved using the ring structure, due to a larger equivalent W/L and lower drain parasitic resistance. In addition, the self-heating effect of LDMOS transistors was also investigated by measuring the pulsed current–voltage (I–V) and pulsed RF characteristics. From the measured results, the ring structure appeared to be a better layout design for RF LDMOS transistors.

Temperature-Dependent Capacitance Characteristics of RF LDMOS Transistors With Different Layout Structures

In this letter, the capacitance characteristics of RF LDMOS transistors with different temperatures and layout structures were studied. In a conventional fishbone structure, the peaks in capacitances decrease with increasing temperature. For the ring structure, two peaks in a capacitance-voltage curve have been observed at high drain voltages due to the additional corner effect. In addition, peaks in gate-to-source/body capacitance decrease and peaks in gate-to-drain capacitance increase with increasing temperature at high drain voltages. By analyzing the effects of temperature on threshold voltage, quasi-saturation current, and drift depletion capacitance, the variations of capacitances with temperature were investigated.

LDMOS Transistor High-Frequency Performance Enhancements by Strain

The effects of mechanical stress on the dc and high-frequency performances of laterally diffused MOS (LDMOS) transistors with different layout structures were investigated by using the wafer bending method. A 3.1% peak cutoff frequency (fT) enhancement is achieved for the multifinger device under 0.051% biaxial tensile strain. For LDMOS with annular layout, the fT enhancement is increased to 3.7% due to the various channel directions. Our results suggest the strain technology can be adopted in LDMOS for RF applications. The transconductance and gate capacitance were also extracted to clearly demonstrate the fT variations.

Enhanced recovery of light-induced degradation on the micromorph solar cells by electric field

The recovery of light-induced degradation of the tandem micromorph solar cell by applying reverse bias is compared with the single-junction amorphous silicon solar cell. The illuminated current density-voltage characteristics and external quantum efficiency show that the degradation of both the micromorph and the amorphous silicon cells can be recovered by applying sufficient reverse bias. The micromorph cell was recovered at smaller reverse bias than amorphous silicon cell. The abundant H in the microcrystalline silicon bottom cell of the micromorph cell can act as a reservoir to repair the defects in the amorphous silicon top cell at the reverse bias. This is responsible for small recovery bias of tandem cells.

Capacitance Characteristics Improvement and Power Enhancement for RF LDMOS Transistors Using Annular Layout Structure

This paper presents an annular-structure lateral-diffused metal-oxide-semiconductor (LDMOS) RF transistor using a 0.5-μm LDMOS process. This paper also examines the dc, small-signal, and large-signal characteristics of RF LDMOS transistors with different closed structures. In particular, the problem of evaluating the LDMOS aspect ratio for annular structure is addressed. The capacitance characteristics improvement in the LDMOS device design using the annular structure was also investigated. The power gain and efficiency of annular structure give nearly 5% enhancement compared to the traditional structure with 80-μm gatewidth at 1.9 GHz. Results show that the annular structure appears to be a better layout design for RF LDMOS transistors.

Analysis of Temperature Effects on High-Frequency Characteristics of RF Lateral-Diffused Metal–Oxide–Semiconductor Transistors

In this work, the effects of temperature on the DC and RF characteristics of lateral-diffused metal–oxide–semiconductor (LDMOS) transistors were studied. Devices with different layout structures were fabricated using a 40 V LDMOS process. The temperature coefficients of the threshold voltage and channel mobility are negative and their values are similar for devices with fishbone and ring structures. In addition, we found that both the cutoff frequency ( fT) and the maximum oscillation frequency ( fmax) decrease with increasing temperature. The variations of fT with different temperatures are not only affected by the change in transconductance but also affected by the drain resistance. Finally, the temperature behaviors of S-parameters were measured, and the ring structure showed less S22 variation with different temperatures than the fishbone structure. We extracted the model parameters of the devices to explain this observation. [DOI: 10.1143/JJAP.47.2650]

Investigation of Hot-Carrier Stress Effect on High-Frequency Performance of Laterally Diffused Metal-Oxide-Semiconductor Transistors

The hot-carrier stress effects on the high-frequency performance characteristics of laterally diffused metal–oxide–semiconductor (LDMOS) transistors were investigated. A constant bias channel hot-carrier stress was applied at room temperature. After applying 3 h of hot-carrier stress, the on-resistance and saturation drain current degradations are 18 and 9%, respectively. However, the degradations of the cutoff frequency and maximum oscillation frequency were less than 2% when the devices were biased before the onset of quasi-saturation. In addition, we found that the degradations of high-frequency parameters are not related to the change in transconductance but to the changes in gate capacitances. Finally, S-parameter variations under hot-carrier stress were also examined in this study. The observations of S-parameter variations are important for RF power amplifier design.