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News 2015

Solar cell publication

A characterization method is presented, which determines fixed charge and interface defect densities in passivation layers. The method bases on a bias voltage applied to an electrode on top of the passivation layer.

During the voltage sweep, the effective carrier lifetime is measured by means of microwave detected photoconductivity. When the external voltage compensates the electrical field of the fixed charges the lifetime drops to a minimum value. This minimum value correlates to Vfb determined in reference impedance measurements. This correlation is measured on p-type silicon passivated by Al2O3 and Al2O3/HfO2 stacks with different fixed charge densities and layer thicknesses. Negative fixed charges with densities of 3.8 x 1012 cm‑2 and 0.7 x 1012 cm‑2 are determined for Al2O3 layers without and with an ultra-thin HfO2 interface. The voltage and illumination dependence of the effective carrier lifetime is simulated with Shockley Read Hall surface recombination at continuous defects and with parabolic capture cross section distributions for electrons and holes. The best match with the measured data is achieved with a very low interface defect density of 1 x 1010 eV‑1cm‑2 for the Al2O3 sample with HfO2 interface.

Novel High k Application Workshop 2015

Similar to the last years, NaMLab invited to the Novel High-k Application Workshop on March 10th, 2015. New challenges offered by the application of high-k dielectric materials in micro– and nanoelectronics were discussed by more than 80 participants from industry, research institutes and universities. NaMLab created with the workshop a stimulating European platform for application-oriented scientist to exchange ideas and discuss latest experimental results on MIM-capacitors, process technology, leakage & reliability as well as characterization of high-k dielectrics integrated in silicon based micro– and nanoelectronics.

New publication

Temperature- and field-induced phase transitions in ferroelectric nanoscale TiN/Si:HfO2/TiN capacitors with 3.8 to 5.6 mol% Si content are investigated for energy conversion and storage applications.

Films with 5.6 mol% Si concentration exhibit an energy storage density of ~40 J/cm3 with a very high efficiency of ~80% over a wide temperature range useful for supercapacitors. Furthermore, giant pyroelectric coefficients of up to -1300 µC/(m2K) are observed due to temperature dependent ferroelectric to paraelectric phase transitions. The broad transition region is related to the grain size distribution and adjustable by the Si content. This strong pyroelectricity yields electrothermal coupling factors k2 of up to 0.591 which are more than one order of magnitude higher than the best values ever reported. This enables pyroelectric energy harvesting with the highest harvestable energy density ever reported of 20.27 J/cm3 per Olsen cycle. Possible applications in infrared sensing are discussed. Inversely, through the electrocaloric effect an adiabatic temperature change of up to 9.5 K and the highest refrigerant capacity ever reported of 19.6 J/cm3 per cycle is achievable. This might enable energy efficient on-chip electrocaloric cooling devices. Additionally, low cost fabrication of these films is feasible by existing semiconductor process technology.

New progress report

Park et al., Ferroelectricity and Antiferroelectricity of Doped Thin HfO2-based Films

The recent progress in ferroelectricity and antiferroelectricity in HfO2 -based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3 , BaTiO3 , and SrBi2Ta2O9 , which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferroelectricity or antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm−2, and their coercive field (≈1–2 MV cm−1) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric fieldeffect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solidstate-cooling, and infrared sensors. Link to paper

NaMLab at Semicon

The largest and most important semiconductor event in Europe, the SEMICON, takes place in October 2015 in Dresden.

Together with 350 exhibitors from 20 countries NaMLab will present its manifold activities in development of material solutions for tomorrow’s electronic devices. The researchers of NaMLab will show new innovations, e.g. in the fields of micro & nanowire devices, energy harvesting, and non-volatile memories.

IEDM Late Submission

Evidence of Single Domain Switching in Hafnium Oxide Based FeFETs: Enabler for Multi-Level FeFET Memory Cells

Recent discovery of ferroelectricity in HfO2 thin films paved the way for demonstration of ultra-scaled 28 nm Ferroelectric FETs (FeFET) as non-volatile memory (NVM) cells. However, such small devices are inevitably sensible to the granularity of the polycrystalline gate oxide film. Here we report for the first time the evidence of single ferroelectric (FE) domain switching in such scaled devices. These properties are sensed in terms of abrupt threshold voltage (VT) shifts leading to stable intermediate VT levels. We emphasize that this feature enables multi-level cell (MLC) FeFETs and gives a new perspective on steep subthreshold devices based on ferroelectric HfO2.


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