Gx Chen

Ultrafast-laser-induced parallel phase-change nanolithography

A phase-change nanolithography technique is developed to fabricate up to millions of two-/three-dimensional nanostructures (∼50nm) over a large area at a high speed by combining femtosecond laser, microlens array, and wet etching process. Near-field scanning optical microscopy, electrical force microscopy, and atomic force microscopy were used to characterize optical and electrical properties of crystalline and amorphous states, respectively. Different reactions of both amorphous and crystalline areas in phase-change film to alkaline solution are demonstrated. Multiphoton absorption and ultrashort pulse contribute to nanostructure generation. This method opens up a route for nanodevice fabrication with phase-change material.

Drive-Current Enhancement in Ge n-Channel MOSFET Using Laser Annealing for Source/Drain Activation

A gate-first self-aligned Ge nMOSFET with a metal gate and CVD HfO 2 has been successfully fabricated using KrF laser annealing (LA) as dopant-activation annealing. By applying an aluminum laser reflector on TaN metal gate, source/drain (S/D) regions are selectively annealed without heating the gate stack. Small S/D resistance and good gate-stack integrity are achieved simultaneously. As a result, a larger drive current and a lower threshold voltage are achieved in Ge nMOSFET using LA activation than that using conventional rapid thermal annealing activation

Germanium n+∕p junction formation by laser thermal process

In this letter, an n+∕p junction on a germanium substrate, formed by phosphorous implantation and subsequent laser thermal annealing process, is demonstrated. The effects of laser energy fluence and irradiation pulse number on the redistribution of dopant atoms have been investigated. The secondary-ion-mass-spectrometry results indicate that steplike dopant profiles are formed with dopant atoms extending deeper upon increased laser energy fluence and successive pulse number. After being irradiated at a laser energy fluence of 0.16J∕cm2 with two successive pulses, the junction exhibits a sheet resistance of ∼50Ohm∕sq for n+ region, a comparable current-voltage characteristic, and much less phosphorus dopant diffusion in comparison with those formed by rapid thermal process annealing.

Determination of thermal parameters of microbolometers using a single electrical measurement

Accurate determination of thermal parameters of microbolometer-based sensors is of considerable interest for many applications. The most important parameters are thermal time constant, heat capacitance and thermal conductance. In this work, we have developed a technique to measure all three quantities using a single electrical measurement. The method involves the measurement of time dependent output voltage of a balanced Wheatstone bridge containing a microbolometer under pulse bias condition. The validity of the approach is verified experimentally using metal–film microbolometers. The experimental results are in excellent agreement with the theoretical analysis of the measurement technique.

On-chip compensation of self-heating effects in microbolometer infrared detector arrays

Abstract It is well known that the signal due to self-heating during read-out of uncooled microbolometers is much larger than that created by incident infrared (IR) radiation to be detected. This results in a degradation of the performance by requiring a large dynamic range of the preamplifier to be allocated for the signal due to self-heating. In this paper, we have studied self-heating during the read-out of microbolometer IR detectors and demonstrated a compensation technique using two microbolometers arranged in a Wheatstone bridge read-out circuit. Finally, the concept is extended for application in focal plane arrays (FPA) and a possible circuit configuration is given to achieve the compensation which may enhance the performance of uncooled detector arrays.

Optical limiting phenomena of carbon nanoparticles prepared by laser ablation in liquids

We report optical limiting properties of carbon nanoparticles, which were made in liquids by laser ablation of a bulk carbon target. The carbon nanoparticles were analyzed with micro-Raman spectroscopy, UV-Vis spectroscopy and Electron microscopy. Optical limiting responses towards 532-nm wavelength were measured with a 7-ns Nd:YAG laser. Nanoparticle size and laser pulse repetition rate effects on optical limiting behaviour were studied. A model was proposed to explain the physical origin of this nonlinear optical process. This work can provide useful information for designing carbon nanoparticle based optical limiters.

OPTICAL LIMITING STUDIES OF NEW CARBON NANOCOMPOSITES AND AMORPHOUS SixNy OR AMORPHOUS SiC COATED MULTI-WALLED CARBON NANOTUBES

By using fluence-dependent transmission measurement with nanosecond laser pulses, we have studied optical limiting (OL) properties of new carbon nanocomposites as well as amorphous SixNy or amorphous SiC coated carbon nanotubes suspended in distilled water. The observed nonlinearity at 532 nm contributed to OL performance of the carbon nanocomposites or carbon nanoballs (CNBs) is suggested to have its origin in the optically induced heating or scattering effects. It is found that when the linear transmittance of the CNBs is less than or equal to 70%, the intensity-dependent transmission of the CNBs is comparable to that of C60. While at 80% linear transmittance, CNBs possess better OL behavior than that of C60. These findings strongly support a potential application of CNBs for all laser protection devices. We have also observed OL effects in the amorphous silicon nitride (a-SixNy) and amorphous silicon carbide (a-SiC) coated multi-walled carbon nanotubes (MWNTs) at wavelengths of 532 and 1064 nm, and found that their OL performances are slightly poorer than that of their parent MWNTs. The possible sources of thickness-dependent OL effects of a-SixNy and a-SiC coated MWNTs are discussed.