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A 2.8μm 4-tap global shutter pixel has been realized for a compact and high-resolution time of flight (ToF) CMOS image sensor. 20,000 e- of high full-well capacity (FWC) per a tap is obtained by employing a supplementary MOS capacitor. 36% of high quantum efficiency (QE) has been achieved by backside scattering technology (BST) and thick silicon process. In addition, demodulation contrast (DC) is improved to 86 % by additional deep photodiode doping process for static potential gradient in a photodiode.

A 0.8 μm-pitch 64 megapixels ultrahighresolution CMOS image sensor has been demonstrated for mobile applications for the first time. Full-well capacity (FWC) of 6k e- was achieved in 0.8 μm pixels as the best in the world, and the advanced color filter (CF) isolation technology was introduced to overcome sensitivity degradation. Dual conversion gain (CG) technology was also first applied to mobile applications to improve the FWC performance of Tetracell up to 12k e-. In addition, highly refined deep trench isolation (DTI) and photodiode design significantly improved dark noise characteristics.

Microstructural reactions of Pd/Ge/Ti/Au contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer have been investigated using cross-sectional transmission electron microscopy, and the results are used to interpret the electrical properties of the ohmic contact. In the as-deposited state, a quaternary phase of PdxAlGaAs containing excess Ge atoms is formed at the interface of Pd/AlGaAs and some microvoids exist at the Pd layer in the vicinity of the interface. When the ohmic metals deposited on the undoped cap layer were annealed, the lowest contact resistivity of 9.1×10−5 Ω cm2 is obtained at 380 °C. AuGa compound is formed at the PdGe/undoped-AlGaAs interface as a result of the reaction between the ohmic metal and the undoped GaAs cap. This is due to the fast in-diffusion of Au toward the undoped AlGaAs through grain boundaries of the PdGe compound. The layer structure is changed to TiO/AuGa/PdGe/AuGa(TiAs+epi-Ge)/undoped-AlGaAs. The AuGa compound en...

Microstructural reactions of PdGe ohmic contact to n-type GaAs were investigated using x-ray diffraction, Auger electron spectroscopy, and slow positron beam. The results were compared with electrical properties to interpret the ohmic contact formation mechanism for the Ge/Pd/n-type GaAs system. The lowest contact resistance of 1.7 Ω mm and the formation of a PdGe compound are observed at the annealing temperature of 240 °C. Slow positron beam results show that Ga vacancies are produced below PdGe during the formation of PdGe ohmic contact to n-type GaAs. This means the existence of n+-GaAs layer below PdGe because Ga vacancy concentration increases with n-type impurity concentration. This supports that the n+-GaAs layer is a regrown layer decomposed from PdxGaAs containing excess Ge atoms during annealing.

Microstructural evidence on the formation of a heavily Ge-doped layer below Pd/Ge-based ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was obtained. The contact resistivity is decreased by two orders of magnitude as InGaAs channel is intermixed. This originates from the formation of Au2Al and Au7Ga2 compounds below the contacts during annealing, via production of group III vacancies. The vacancies play a role in producing free electrons by the incorporation of Ge atoms, resulting in intermixing of InGaAs as well as reduction of contact resistivity.

Microstructural evidence on direct contact of Au/Ge/Ni/Au ohmic metals to a InGaAs channel in AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer was found using transmission electron microscopy, and the results were used to interpret the electrical properties of the contact. The lowest contact resistivity of 3.8×10−6 Ω cm2, obtained at 420 °C annealing, is due to the penetration of the interfacial compounds, Au2Ga and Au2Al, into the buried InGaAs channel. The direct contact of the compounds to the channel causes the reduction of series resistances between the ohmic compounds and the channel, resulting in the low contact resistivity.

The Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was investigated with the etch depth of an undoped GaAs/AlGaAs cap layer. The contact resistivity decreases from 9.5×10−5 to 2.3×10−6 Ω cm2 when the contacts were formed on a n-Al0.23Ga0.77As layer by removing the undoped cap layer. X-ray diffraction results show that the good ohmic contact is due to the formation of Au2Al as well as β-AuGa. Both compounds play a role to create group-III vacancies, followed by the incorporation of Ge into group-III vacancies, namely, creation of free electron below the contact. This results in the considerable elimination of contact resistivity by lowering the effective tunneling barrier.

A standby current failure of the 80nm design-ruled Dynamic Random Access Memory (DRAM) during burn-in stress was investigated. In our case, hot electron induced punch-through (HEIP) of a PMOS transistor was a leakage current source. The bake test is a useful method to identify the mechanism of a standby current failure due to hot carrier degradation.

Microstructural reactions of a Pd/Ge contact to a AlGaAs/InGaAs pseudomorphic high electron mobility transistor (PHEMT) have been investigated, and the results have been used to interpret the changes of electrical properties of the PHEMT. In the as-deposited state, a ternary phase of Pd x GaAs containing excess Ge atoms is formed at the interface of Pd/GaAs. When the ohmic metals deposited were annealed at 300°C, a PdGe compound was formed and its contact resistivity was decreased to 1.2×10-7 Ω·cm2. This is due to the preferential outdiffusion of Ga atoms to the PdGe during annealing, leaving Ga vacancies behind. Simultaneously, Ge atoms are indiffused to the GaAs and occupy the Ga vacancies, converting the interfacial GaAs layer into n+-GaAs. The low-temperature PdGe ohmic contact allows changing the sequence in the formation of source/drain and gate electrodes in the PHEMT process. The device performance was remarkably improved as the annealing temperature was increased or the contact resistivity was reduced. The PHEMTs with a gate length of 1.1 µm, annealed at 300°C, exhibit maximum transconductance of 381 mS/mm.

The effect of existence of undoped GaAs/AlGaAs cap layers on Ohmic contact resistivity in an AlGaAs/InGaAs pseudomorphic high electron mobility transistor was investigated. The Au/Ge/Ni/Au Ohmic contact formed on the undoped GaAs cap layer yields the lowest contact resistivity of 3.8×10−6 Ω cm2. Meanwhile, the contact resistivity increases a little to 5.0×10−6 Ω cm2 for the contacts formed on an n-Al0.23Ga0.77As layer exposed by removing the undoped cap layer. Both contact resistivities are comparable to those obtained using the n+-GaAs cap layer. The good Ohmic contacts obtained independent of removal of the undoped cap layer are due to the formation of the interfacial compounds, Au2Al and Au2Ga, during annealing. The interfacial compounds penetrate deep into the buried InGaAs channel, resulting in direct contacts to the channel.

The contact resistance degradation mechanism of the Pd/Ge ohmic contact on a pseudomorphic high electron mobility transistor was interpreted. The contact resistance continuously degrades at temperatures higher than 300 °C although no microstructural changes were observed. Meanwhile, elemental Ga atoms were preferentially outdiffused to the PdGe layer and Ge atoms were indiffused to the GaAs during annealing. The indiffused Ge converts the interfacial GaAs layer into n-GaAs, in which Ga vacancies are produced to maintain the charge neutrality condition. The Ga vacancy concentration further increases with annealing temperature, which plays a role in degrading the contact resistance as a result of the recombination of electrons with the Ga vacancies.