Giuseppe Cocorullo

Temperature dependence of the thermo-optic coefficient in crystalline silicon between room temperature and 550 K at the wavelength of 1523 nm

The temperature dependence of the thermo-optic coefficient for crystalline silicon has been measured in the temperature range between room temperature and 550 K at the wavelength of 1523 nm by means of an interferometric technique. This technique, which requires a very simple experimental setup, is based on the observation of the fringe pattern produced by temperature changes in a Fabry–Perot resonator. Measurement results indicate that the thermo-optic coefficient is independent on the sample doping and crystal plane orientation. The experimental data appear to be in agreement with the few values reported to date at this important wavelength. The temperature dependence of the excitonic band gap is also calculated by fitting these data with a recently introduced model of ∂n/∂T.

Amorphous silicon waveguides and light modulators for integrated photonics realized by low-temperature plasma-enhanced chemical-vapor deposition.

A new amorphous silicon waveguide is realized by use of amorphous silicon carbon as cladding material. The structure is characterized both experimentally and theoretically, and its application for optical interconnections in photonic integrated circuits on silicon motherboards is proposed. The fabrication process is based on low-temperature (220 degrees C) plasma-enhanced chemical-vapor deposition and is compatible with standard microelectronic processes. Propagation losses of 1.8 dB/cm have been measured at the fiber-optic wavelength of 1.3 microm. A strong thermo-optic coefficient has been measured in this material at this wavelength and exploited for the realization of a light-intensity modulator based on a Fabry-Perot interferometer that is tunable by temperature.

Amorphous silicon-based guided-wave passive and active devices for silicon integrated optoelectronics

Waveguides and interferometric light amplitude modulators for application at the 1.3- and 1.55-/spl mu/m fiber communication wavelengths have been fabricated with thin-film hydrogenated amorphous silicon and its related alloys. The technique adopted for the thin-film growth is the plasma- enhanced chemical vapor deposition, which has been shown to give the lowest defect concentration in the film. Consequently the proposed waveguiding structures take advantage of the low optical absorption shown by a-Si:H at photon energies below the energy gap. In addition a good radiation confinement can be obtained thanks to the bandgap tailoring opportunity offered by this simple and inexpensive technology. In particular rib waveguides, based on a a-SiC:H/a-Si:H stack, have been realized on crystal silicon, showing low propagation losses. Recently, however, a new interest as low as 0.7 dB/cm. The same structure has been utilized for the fabrication of thermooptic Fabry-Perot modulators with switching times of 10 /spl mu/s. Modulators based on the alternative waveguiding configuration ZnO/a-Si:H, giving comparable results, are also presented.

Temperature dependence of the thermo-optic coefficient of InP, GaAs, and SiC from room temperature to 600 K at the wavelength of 1.5 μm

The thermo-optic coefficient ∂n/∂T has been measured from room temperature to 600 K at the wavelength of 1523 nm in three important semiconductors for fiber-optic device fabrication, namely, InP, GaAs, and 6H–SiC. The adopted technique is very simple and is based on the observation of the periodicity of the signal transmitted, at the desired wavelength, by an etalon made of the material under test, when it experiences a temperature variation. The values of ∂n/∂T measured in InP and GaAs at room temperature are in agreement with previously reported ones, but increase with temperature with a weak quadratic dependence. SiC conversely shows a lower thermo-optic coefficient (2.77×10−5 K−1) at 300 K, which, however, doubles for a 300 K temperature increase.

Temperature dependence analysis of the thermo-optic effect in silicon by single and double oscillator models

The thermo-optic coefficient (dn/dT) of crystalline silicon has been critically analyzed in the temperature range 300–600 K, at the fiber optic communication wavelength of 1.5 μm. The temperature dependence has been attributed to the variation of the interband transition energies at some critical points of the silicon band structure. The experimental data have been fitted using single and double oscillator models. In particular, the double oscillator model, which is physically correlated to the silicon band structure, has been exploited to extrapolate the temperature dependence of the interband transition energies at some points (critical points) of the combined density of states. The extracted parameters are in good agreement with the data reported in the literature. Finally, in connection with both of the oscillator approximations, an analysis based on thermodynamic considerations is carried out, and electron–hole formation entropy and specific heat are calculated. The consistency of the obtained result...

Silicon thermooptical micromodulator with 700-kHz -3-dB bandwidth

A silicon Fabry-Perot waveguide modulator, operating at the fiber optic communication wavelengths of 1.3 and 1.55 /spl mu/m, has been entirely fabricated using microelectronic techniques. The planar optical cavity has been defined by plasma etching and has a length of 100 /spl mu/m. The device, based on the thermooptic effect, is electrically driven and exhibits a maximum modulation depths of 60%. The measured -3 dB bandwidth is 700 kHz, which is by far the best result ever reported, to our knowledge, for thermooptic effect based modulators.<<ETX>>

Design Procedure for Settling Time Minimization in Three-Stage Nested-Miller Amplifiers

Low-power, low-voltage, and high-performance requirements are badly needed for operational amplifiers (op-amps) in modern applications. In this brief, a design method for minimizing the settling time in three-stage nested-Miller schemes is presented. As an application example, a CMOS 0.35-mum voltage follower with 115-dB dc gain and fastest step response to 1% accuracy level, is designed. Circuital simulations demonstrate that the proposed procedure allows the amplifier settling-time/power-consumption ratio to be significantly improved with respect to conventionally designed op-amps.

A temperature all-silicon micro-sensor based on the thermo-optic effect

A new class of temperature silicon micro-sensors, based on an interferometric optical technique, is presented. The sensing element consists of a planar Fabry-Perot cavity defined on a silicon wafer by highly anisotropic reactive ion etching, and is therefore suitable for full integration with other standard opto- and micro-electronic devices. Preliminary temperature measurements have been performed with the temperature resolutions predicted by the theory. The limit performances, in terms of resolution, speed of operation and energy dissipation of this class of sensors are discussed in detail. In particular, a final temperature resolution of 0.064/spl deg/C is expected for a low loss interferometric cavity, with a settling time of 150 ns and a 0.2% readout error. An energy resolution as low as 30 nJ is also estimated.

Area-Delay Efficient Binary Adders in QCA

As transistors decrease in size more and more of them can be accommodated in a single die, thus increasing chip computational capabilities. However, transistors cannot get much smaller than their current size. The quantum-dot cellular automata (QCA) approach represents one of the possible solutions in overcoming this physical limit, even though the design of logic modules in QCA is not always straightforward. In this brief, we propose a new adder that outperforms all state-of-the-art competitors and achieves the best area-delay tradeoff. The above advantages are obtained by using an overall area similar to the cheaper designs known in literature. The 64-bit version of the novel adder spans over 18.72 μ2 of active area and shows a delay of only nine clock cycles, that is just 36 clock phases.

Thermo-optic effect exploitation in silicon microstructures

The strong thermo-optic effect in silicon has been exploited for the fabrication of new sensing and communication devices. A temperature sensor, an electromagnetic energy sensor and an optical modulator are in particular presented. These devices, all working on interferometric principles, have been realized by means of the silicon standard microelectronic technologies, and are therefore suitable for full integration with on-chip circuitry. New thermo-optical materials are finally proposed with superior characteriztics, which still maintain the compatibility with VLSI technology.