M. Benzohra

Using microchannels to cool microprocessors: a transmission-line-matrix study

Abstract As microprocessors components density and clock frequency increase, so do heat dissipation. The heat results from Joule effect due to leakage currents in the components area or active region. This region is only few microns thick and can quickly reach destructing temperatures if heat is not quickly removed. On this critical issue depends the system reliability. The active region is separated from the ventilated heat sink by a silicon substrate and a metal integrated heat spreader, both hundreds of microns thick. This interface region is the microprocessors heat transfer plate where heat exchange is achieved by conduction. Because of the localized heat source, the thermal spreading resistance of the interface region can be high. A novel way of spreading heat in that region is the use of microchannel arrays where an appropriate thermal compound or a phase change liquid can be trapped to increase heat transfer by conduction or to create micro-heat-pipes. Traditional cooling methods, with conventional and well optimised heat sinks, can then be used with less burden. In this paper, the Transmission-Line-Matrix (TLM) technique is used to simulate the effect of microchannels on the temperature distribution in the active region. To minimize the interface heat resistance various microchannel and patterns are examined. In this part of the work, the microchannels are filled with the heat spreader material copper or aluminium. The results show an improved thermal transient behaviour and a reduced active region temperature in steady state.

Deep levels induced by low energy B+ implantation into Ge-preamorphised silicon in correlation with end of range formation

Abstract It is well established that low energy B+ ion implantation into Ge- (or Si) implantation pre-amorphised silicon allows ultra-shallow p+n junctions formation. However, this process is known to generate defects such as dislocation loops, vacancies and interstitials which can act as vehicles to different mechanisms inducing electrically active levels into the silicon bulk. The junctions studied have been obtained using 3 keV/ 10 15 cm −2 B + implantation into Ge-implantation pre-amorphised substrates and into a reference crystalline substrate. Accurate measurements using deep level transient spectroscopy (DLTS) and isothermal transient capacitance ΔC(t,T) were performed to characterise these levels. Such knowledge is crucial to improve the device characteristics. In order to sweep the silicon band gap, various experimental conditions were considered. The analysis of DLTS spectra have first showed three deep levels associated to secondary induced defects. Their concentration profiles were derived from isothermal transient capacitance at depths up to 3.5 μm into the silicon bulk and allowed us to detect a new deep level. The evolution of such defect distribution in correlation with the technological steps is discussed. The end of range (EOR) defect influence on electrical activity of secondary induced defects in ultra-shallow p+n diodes is clearly demonstrated.

On the use of the matrix pencil method for deep level transient spectroscopy: MP-DLTS

A new approach to capacitance transient analysis, based on the matrix pencil (MP) method, is proposed for deep level transient spectroscopy (DLTS) (MP-DLTS). The MP method offers the least statistical variance of the estimates in the presence of noise. Simulation tests have shown this method to lead to a significant improvement in DLTS resolution even for low trap concentrations. Its noise sensitivity and resolution are quantified and compared with five different DLTS analysis techniques. The MP-DLTS method is found to outperform both DLTS spectrum and direct transient analysis techniques. An experimental investigation of the electrically active defects induced by a germanium preamorphization step prior to dopant implantation was undertaken using the MP-DLTS method. Two electron traps were detected in all samples and characterized.

Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon: the case of BF2+ implantation

We have simulated transient enhanced diffusion (TED) in the presence of end-of-range (EOR) defects produced by Ge amorphization followed by BF2 implantation. Ostwald ripening of EOR defects has been taken into account. A comparison of annealed profiles with equivalent B implantation shows that the existing models are not sufficient to simulate the BF2 experimental profiles where the boron diffusion depth is very low. We have proposed that the presence of fluorine can act as sinks for interstial boron and, hence, reduces the boron diffusion depth in order to obtain a good approximation of experimental profiles.

Magnetic susceptibility of P+N junctions in correlation with the nature of silicon substrate: crystalline or pre-amorphised

Abstract Ge pre-amorphisation step is used to reduce the high diffusivity and the transient-enhanced diffusion of boron implanted in silicon. The aim of the process is to obtain shallow P + N junctions. The pre-amorphisation step was performed under different conditions (in ambient temperature and in nitrogen). Following the rapid thermal annealing step, end of range (EOR) defects appear at the amorphous–crystalline interface. These defects could influence the electrical characteristics of the P + N junctions. An experimental study concerning three samples has been performed without and under a magnetic field of 800 G. The magnetic susceptibility was essentially observed in the case of the reverse current. The impact of the magnetic field, studied by varying the sample temperature, permits us to show an increase of the magnetic susceptibility when the defects present in such structures are electrically active. These results are discussed in comparison with their deep-level transient spectroscopy (DLTS) spectra.

Design of a Compliant Underactuated Robotic Finger With Coordinated Stiffness

In this paper, we propose an underactuated robotic finger whose grasp behavior is modulated by the design of its superelastic joints. Using shape-memory alloy, the finger joints can be given specific stiffness and pre-form shapes such that a single-cable actuation rather than opposing-pair actuation can be used; this also allows the grasping motions of the phalanges to be synchronized in the free phase and then adaptive once contact is made. A default-closed pre-tensioned configuration allows grasp forces to be maximal for larger objects and still keeps control components such as tendons out of the grasp workspace. The simplicity of the design lends itself to the possibility of integrated joint angle and surface pressure sensing on the finger itself. The details of design, prototyping and testing are described.© 2013 ASME

Thermal behavior Spice study of 6H-SiC NMOS transistors

Silicon carbide is a material that is undergoing major advances associated with a broad scope in the field of electronics. The main properties of silicon carbide such as its high thermal conductivity and high band gap make it a material suitable for use in high-temperature and high-power applications. In this Spice study, the thermal behavior of 6H-SiC NMOS transistors is analyzed through their conductance and transconductance changes with temperature in the range -200 to 700^oC. The performances in two basic applications, current mirrors and differential amplifiers, are compared to similar circuits with silicon transistors. The results show that the 6H-SiC NMOS transistors can be used up to 700^oC, while those based on silicon transistors are limited to around 160^oC.

Electrical characterizations of preamorphized junctions under LF magnetic field

Abstract The increased requirements for reduction of electronic system dimensions, essentially in embedded equipment such as automotive and avionics, lead to juxtapose high power modules and low level modules on the same printed circuit. This juxtaposition induces electromagnetic perturbations that can disturb or damage the operation of the system. In order to study thoroughly these phenomena, a low frequency (LF) magnetic field was applied to shallow P+N junctions obtained by the preamorphization technique, at two temperatures: ambient and nitrogen temperature. Electrical characterizations were performed on the different samples. The results show that the impact of the LF magnetic field is essentially observed in the generation-recombination region of the junction. Moreover, it appears that crystalline sample presents a good immunity to the LF magnetic field perturbation at high temperature. On the other hand, the preamorphization temperature influences the response of the sample. So, a good control of the technological parameters will permit to reduce or cancel the effect of the magnetic perturbations on the electronic components since conception.

Thermal behaviour of 6H–SiC bipolar transistors: spice simulation and applications

Abstract As material quality improves and growth technology develops, SiC BJTs are regaining interest. They have the advantage of carrier modulation, high current capabilities and lower initial voltage drop. In this work, the thermal behaviour of 6H–SiC bipolar transistors is simulated. The examined figures of merit such as input resistance h 11 , current gain β and transconductance g m show superior performance of 6H–SiC BJTs, at high temperatures, when compared to similar silicon counterparts. In the range of temperatures −20 to 160 °C, drawbacks found in Si BJTs are attenuated or eliminated with the use of SiC BJTs. These advantages are transferred to 6H–SiC based circuits. The built current mirror shows quasi-ideal behaviour while the designed input stage of the amplifier has a voltage gain thermally stabilised up to 140 °C.

Reliable Measurements of Defect Profiles in Low-Energy Boron Implanted Silicon

Low-energy implantation is one of the most promising options for ultrashallow junction formation for the new generation of bipolar complementary metal oxide semiconductor (BiCMOS) silicon technology. Boron is one of the dopants to be implanted, but is the most problematic because of its low stopping power, and its tendency to undergo transient enhanced diffusion and clustering during thermal activation. In this paper we report an experimental contribution, using secondary defect profiles, to the understanding of low-energy B implants in crystalline silicon. Shallow p+n junctions were formed by low-energy B implantation – 1015 cm-2 at 3 KeV – into n-type crystalline silicon preamorphized with germanium – 1015 cm-2 at 30 KeV, 60 keV and 150 keV. Rapid thermal annealing (RTA) for 15 s at 950°C was then performed to achieve electrical activation of the dopant and implantation damage removal. We propose a reliable approach to the measurement of secondary defect profiles, induced by this process, using isothermal transient capacitance associated with deep-level transient spectroscopy (DLTS). This approach could be generalised to the profile measurement of any defect detected into silicon or III–V semiconductor substrate. In our case, we obtain a relatively high concentration of B-related electrically active defects to a depth of 3.5 µm in the crystalline silicon bulk.