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•Development of half skeleton structures for silicide-based thermoelectric modules.•Fabrication of twenty-two (four legs) silicide-based thermoelectric modules.•Excellent ...repeatability of the achieved output power.•State of the art power density performance.•Use of mass-produced materials and simple fabrication tools.
Silicide-based materials are among the most promising candidates for a mass manufacturing of thermoelectric devices allowing converting waste heat into electricity in the medium temperature range (250–500 °C), as they are formed from abundant, low cost and non-toxic elements while exhibiting good thermoelectric properties. In order to manage the detrimental mismatch of thermal expansion coefficients between the n and p-type materials constituting the thermoelectric legs, inducing thus thermomechanical stresses, we propose in this paper a new design of modules having a 'half-skeleton' structure. Twenty-two modules consisting of two couples of thermoelectric legs combining n-type magnesium silicide Mg2(Si, Sn) and p-type higher manganese silicide have been fabricated according to this design, the thermoelectric materials being manufactured by kilograms. It is clearly shown that all the interfaces present in the modules are free from cracks, oxygen, and diffusion. The remarkable repeatability of the measured thermoelectric performance attests the robustness of our manufacturing process. An average power output of 0.37 W has been achieved, i.e. a power density of 0.95 W/cm2, for a temperature difference of 400 °C (hot side temperature of 450 °C), placing our modules at the state of the art level while using simple production tools and materials mass production. Comparing this performance to finite elements modelling, the performance could be even enhanced. Long term stability tests at a given temperature and under cycling conditions in different working atmospheres are underway.
Understanding the thermal stability of the Mg2(Si,Sn) system is essential to define their safe temperatures of service. Despite its good thermoelectric performance, Mg2(Si,Sn) is subject to a phase ...separation during thermal cycling due to the miscibility gap, which leads to a degradation of its thermoelectric properties and affects its performance during device operation. Isothermal annealing at 500 °C and 750 °C were performed with different annealing time to investigate thermal stability of Mg2(Si,Sn). During the heat treatment, two phases were formed associated with porosity in the matrix. In addition, thickness of specimen was tracked and a significant expansion was detected. This phenomenon is attributed to the Kirkendall effect. The composition and the structure of the two forming phases were investigated by electron probe microanalysis and X-ray diffraction. Finally, the optimized thermal treatment allowed to stabilize the Mg2(Si,Sn) without porosity and the presence of two thermodynamically stabilized phase (Mg2Si0.41Sn0.59 and Mg2Si0.58Sn0.42) leading to a better reliability of the silicide thermoelectric modules.
•This article is a full length article and not a review paper.•According to the submission website and the instruction for authors the highlights are not requested only for review papers.•However, to the finalization step to build the pdf they are requested.•This is why I submit this file.
Some of the energy used in transportation and industry is lost as heat, often at high-temperatures, during conversion processes. Thermoelectricity enables direct conversion of heat into electricity, ...and is an alternative to the waste-heat-recovery technology currently used, for example turbines and other types of thermodynamic cycling. The performance of thermoelectric (TE) materials and modules has improved continuously in recent decades. In the high-temperature range (
T
hot side
> 500°C), silicon–germanium (SiGe) alloys are among the best TE materials reported in the literature. These materials are based on non-toxic elements. The Thermoelectrics Laboratory at CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) has synthesized
n
and
p
-type SiGe pellets, manufactured TE modules, and integrated these into thermoelectric generators (TEG) which were tested on a dedicated bench with hot air as the source of heat. SiGe TE samples of diameter 60 mm were created by spark-plasma sintering. For
n
-type SiGe doped with phosphorus the peak thermoelectric figure of merit reached
ZT
= 1.0 at 700°C whereas for
p
-type SiGe doped with boron the peak was
ZT
= 0.75 at 700°C. Thus, state-of-the-art conversion efficiency was obtained while also achieving higher production throughput capacity than for competing processes. A standard deviation <4% in the electrical resistance of batches of ten pellets of both types was indicative of high reproducibility. A silver-paste-based brazing technique was used to assemble the TE elements into modules. This assembly technique afforded low and repeatable electrical contact resistance (<3 nΩ m
2
). A test bench was developed for measuring the performance of TE modules at high temperatures (up to 600°C), and thirty 20 mm × 20 mm TE modules were produced and tested. The results revealed the performance was reproducible, with power output reaching 1.9 ± 0.2 W for a 370 degree temperature difference. When the temperature difference was increased to 500°C, electrical power output increased to >3.6 W. An air–water heat exchanger was developed and 30 TE modules were clamped and connected electrically. The TEG was tested under vacuum on a hot-air test bench. The measured output power was 45 W for an air flow of 16 g/s at 750°C. The hot surface of the TE module reached 550°C under these conditions. Silicon–germanium TE modules can survive such temperatures, in contrast with commercial modules based on bismuth telluride, which are limited to 400°C.
The feasibility of split capacitance-voltage (C-V) measurements in sub-0.1 μm Si MOSFETs is demonstrated. Based on the split C-V measurements, an improved methodology to extract accurately the ...effective channel length and the effective mobility is proposed. Unlike conventional I/sub d/(V/sub g/)-based extraction techniques, this new approach does not assume the invariance of the effective mobility with gate length (assumption proved to be false in this paper). This method is relevant to study transport limitations in ultimate MOSFETs as illustrated with the study of pocket implant influence on 50-nm p-MOSFETs.
This paper presents an experimental study of a STEG (solar thermoelectric generator) working at high concentration ratio (>100) and high temperature (≥450 °C). An indoor characterization set-up based ...on Si80Ge20 thermoelectric material coupled with a selective absorber and a solar concentrating simulator was developed. The goal was to validate a physical model allowing to predict performances of such thermoelectric material for much higher temperatures. Predictive efficiencies were thus extrapolated for a working temperature beyond 800 °C. The critical issue deals with the best system dimensioning taking into account the concentrator size, and the efficiency versus the TEG (thermoelectric generator) size.
•Experimental study of Solar Thermoelectric Generator working at high temperature.•Characterization of Si80Ge20 thermoelectric material coupled with TiAlN absorber.•Development of a predictive physical model for much higher temperatures.•Modeling of electric power generated by a thermoelectric cascaded device.
► Biasing the back interface in accumulation while extracting carrier mobility in FD-SOI MOSFETs leads to underestimated values. ► Apparent mobility degradation with decreasing film thickness in ...ultra-thin SOI MOSFET or Pseudo-MOSFET measurement is due to an additional component of the vertical electric field. ► In Pseudo-MOSFET measurements, the additional component of the vertical electric field comes from the traps and charges at the free-surface of the sample. ► We propose a new model to take this additional component of the vertical electric field into account.
The mobility-thickness dependence in SOI films is clarified. Measurements in fully depleted SOI MOSFETs show that the low-field mobility at the front channel decreases by thinning the Si film or by sweeping the back gate from depletion into accumulation. We demonstrate that this mobility degradation is only apparent, being related to the potential value at the surface facing the channel. This opposite-surface potential induces an intrinsic vertical field which adds to the usual gate-related field. The mobility drop simply indicates a deviation from the low-field condition which cannot be achieved. We propose an updated model for proper extraction and interpretation of the low-field mobility. Pseudo-MOSFET results reveal the existence of a similar additional vertical field in bare SOI wafers, induced by charges present on the unpassivated surface. This intrinsic field increases in thinner films and affects pseudo-MOSFET conduction. The mobility decrease measured in SOI wafers with thinner films reflects the increasing impact of the intrinsic field and does not imply any degradation in quality of film-BOX interface.
The feasibility of split
C–
V measurements is successfully demonstrated on sub-0.1
μm Si MOSFETs. A novel improved methodology to extract accurately the effective channel length and the effective ...mobility is thus proposed. Unlike conventional
I
d(
V
g) based extraction techniques, this new approach does not assume the invariance of the effective mobility with gate length. The method is successfully applied to advanced Si and SiGe PMOSFETs down to 50
nm.
In this brief, the hole transport properties of narrow-width germanium-on-insulator (GeOI) pMOSFETs are investigated. We report, for the first time, +65% low-field hole mobility enhancement in ...narrow-width (0.29-mum effective width W eff ) versus large-width (10- mum W eff ) GeOI mesa-isolated devices. The observed enhancement, which is independent of the device length down to 90 nm, is attributed to improved sidewall transport properties resulting in higher hole mobility on the sides than on the top of the devices. At high inversion charge density N inv ~ 10 13 cm -2 , + 55% hole effective mobility improvement is preserved. The top and side low-field mobilities ( mu top and mu side , respectively) were extracted, showing + 90% mobility improvement at the sides (mu top = 125 cm 2 /V middots -1 and mu side = 240 cm 2 /V middots -1 ).
The origin of parasitic leakage that occurs in some GeOI pMOSFETs has been investigated and located at the Ge-buried oxide (BOX) interface. Silicon passivation of that interface was found to be ...effective in reducing this current. An optimum thickness of the buried silicon capping is required to reduce the parasitic leakage current while preserving Ge-like back channel transport properties.
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