Chang-Da Tsai

Local melting induced by electromigration in flip-chip solder joints

A new electromigration failure mechanism in flip-chip solder joints is reported. The solder joints failed by local melting of a PbSn eutectic solder. Local melting occurred due to a sequence of events induced by the microstructure changes in the flip-chip solder joint. The formation of a depression in the current-crowding region of a solder joint induced the local electrical resistance to increase. The rising local resistance resulted in a larger Joule heating, which, in turn, raised the local temperature. When the local temperature rose above the eutectic temperature of the PbSn solder, the solder joint melted and consequently failed. The results of this study suggest that a dynamic, coupled simulation that takes into account the microstructure evolution, current density distribution, and temperature distribution may be needed to fully solve this problem.

X-ray photoelectron spectroscopy study of (NH4)2Sx-treated Mg-doped GaN layers

We present here the passivation mechanism and the chemistry of an (NH4)2Sx-treated Mg-doped GaN surface examined by using x-ray photoelectron spectroscopy. The native oxide on the GaN surface can be removed by the (NH4)2Sx treatment process. The S atoms not only bond as elemental sulfur and disulfides, but occupy nitrogen-related vacancies.

Thermal reliability and characterization of InGaP Schottky contact with Ti/Pt/Au metals

Abstract We present the characteristics of Ti/Pt/Au Schottky contacts on wide bandgap InGaP semiconductors with surface pre-treatment before Schottky contact deposition, and investigate the influence of post heat treatment on Schottky diodes. With the pre-deposition surface etching by dilute HCl, dilute NH 4 OH, or buffer oxide etchant (BOE), the performance of Schottky diodes compared with samples without surface pre-treatment is improved significantly. Auger electron spectroscopy (AES) analysis of the thermally annealed Schottky diode has been performed to investigate the failure mechanism. No significant change was found for samples annealed up to 450°C. However, a drastic degradation of the barrier height and the ideality factor was observed in samples annealed at 500°C, which may be caused by the interdiffusion and penetration of metals into the semiconductor.

High performances and reliability of novel GaAs MSM photodetectors with InGaP buffer and capping layers

To avoid the trap-induced, low-frequency internal gain and improve the reliability for thermal storage test, a novel structure of GaAs metal-semiconductor-metal photodetector with InGaP buffer and capping layers is investigated. The dark current density of the photodetectors is about 7 /spl mu/A/cm/sup 2/. Its responsivity at 0.83-/spl mu/m wavelength is about 0.48 A/W. After thermal storage at 150/spl deg/C for 10 h, no performance degradation was found in the novel photodetectors.

Improved performances of InGaP Schottky contact with Ti/Pt/Au metals and MSM photodetectors by (NH4)2Sx treatment

Abstract To extend the high performances of the GaAs MSM photodetectors with InGaP buffer and capping layers, the (NH 4 ) 2 S x treatment of InGaP is investigated. The surface states are reduced by sulfur passivation. Whereupon, the performances of InGaP Schottky contact with Ti/Pt/Au metals are improved. The improved dark current and insensitive responsivity with incident optical power are demonstrated by suitable process control of sulfur passivation.

Study of InGaP/GaAs/InGaP MSM photodetectors using indium–tin–oxide as transparent and antireflection Schottky electrode

Abstract We report the performance of InGaP/GaAs/InGaP metal–semiconductor–metal photodetectors (MSM-PDs) using indium–tin–oxide (ITO) as transparent and antireflection Schottky electrode. The dark current and photoresponsivity of about 60 pA (i.e. 2.4 μA cm −2 ) and 0.58 A W −1 at 5 V bias for a 50×50 μm 2 photosensitive area with 2 μm fingers and spaces were measured. We demonstrated that the corresponding rise time, fall time, full width at half maximum and 3 dB bandwidth of temporal responses were 26.4, 134.6, 44.6 ps and 7.0 GHz, respectively. The results of InGaP/GaAs/InGaP MSM-PDs with an ITO Schottky electrode were compared to those of identical geometry devices fabricated with a Ti/Pt/Au Schottky electrode.

Sidegating effect improvement of GaAs metal–semiconductor field effect transistor by multiquantum barrier structure

The sidegating effect in a GaAs metal–semiconductor field effect transistor is significantly suppressed by the use of a multiquantum barrier (MQB) structure as a buffer layer. The enhancement of potential barrier height of the MQB buffer layer is confirmed from the comparison with a heterostructure buffer layer device.

Electromigration induced metal dissolution in flip-chip solder joints

The failure of flip chip solder joints through the dissolution of the Cu metallization was studied. From the location and geometry of the dissolved Cu, it can be concluded that current crowding played a critical role in the dissolution. It can also be concluded that temperature, as an experimental variable, is not less import than the current density in electromigration study. Experimentally, no evidence of mass transport due to thermomigration was observed.

Nonalloyed GaAs metal-semiconductor field effect transistor

Abstract A novel GaAs metal-semiconductor field-effect transistor (MESFET) with Al 0.25 Ga 0.75 As/GaAs multiquantum barrier (MQB) buffer layer and narrow band InAs/graded InGaAs capping layer was demonstrated. The MQB buffer layer can improve the sidegating effect and isolation. The capping layer can perform nonalloy ohmic contact with Ti/Pt/Au metals. Furthermore, the Ti/Pt/Au metals directly contact with GaAs active channel layer can work as Schottky barrier. For the fabrication of this novel MESFET, the thermal alloy and alignment processes can be avoided.

High performance of InGaP/GaAs MSM photodetectors using Cu/Au Schottky contact

We present the high performance of InGaP/GaAs metal- semiconductor-metal photodetectors (MSM-PDs) using copper as the interdigital Schottky electrodes. The devices exhibit ultra-low dark current (70 pA at bias of 10 V) and ultra- fast pulse response (over 9 Ghz). The notable dark current characteristic and the absence of trap-induced gain are accredited to the superior properties of InGaP capping layer. The superior performances of InGaP/GaAs MSM-PDs make it promising for data communication.