Selected Research Projects
Graphene, the two-dimensional form of carbon, is considered one of the most promising materials for future IT applications. This is due to the material's special properties: it is almost as hard and durable as diamond, but can be stretched like rubber. It outperforms copper as a conductor of heat and silicon as a conductor of electricity. It is virtually invisible, as it is composed of a single layer of carbon atoms. It is chemically resilient, impermeable to most substances, and based on carbon, a readily available material.
By now, graphene can be produced in large quantities, and possible applications are beginning to be developed: the material may be used as an “electronic ink” to produce electronic circuits, or provide the basis for foldable cell phone displays. Planned are new ultra-fast transistors, superfast optocouplers, as well as new concepts for quickly rechargeable batteries, the sequencing of DNA strands, and even water desalination facilties.
In RAMs (Random Access Memories), the cells are arranged in a matrix for storing information. This structure enables very fast access to the individual cells - regardless of the location in the matrix where the information is or is to be stored. The main memories used in computers today are Dynamic RAMs (DRAMs) whose information is based on the charge states of small capacitors. Due to self-discharging processes, the capacitors must be refreshed in fractions of a second. Despite their excellent performance, DRAMs have the disadvantage of volatility: when the power supply is switched off, the stored information is lost. This significantly limits the speed at which computers or smartphones "boot up", on the one hand, and the general use in portable devices, on the other.
Non-volatile memories are now available with flash memories in high memory densities up to 128 Gbit. However, due to the slow write times (several 100 microseconds), the limited number of write cycles (105) and the high operating voltages (12-18 V), this class is not suitable for use as working memory.
There are a number of fundamentally new approaches to combining the advantages of DRAM and Flash. The most promising alternative concept for future information storage is the redox-based resistive RAM (ReRAM). An essential component of such a memory cell is an element which typically consists of a very thin metal oxide layer between electrode materials and which can be switched between two or more different stable resistance states by the direction of the applied voltage via a certain threshold voltage. Their properties combine non-volatility with high write and access speeds, a non-destructive read-out, very high integration densities and low energy consumption. At the Institute of Materials of Electrical Engineering II, the physicochemical understanding of the resistive switching effect on the atomic scale is investigated in detail. ReRAM oxide cells are highly complex systems that raise numerous questions about the non-linearity of switching kinetics, the interrelation between ionic and electronic charge transport on the nanometer scale, the geometry of the switching areas, the effect of extremely high electric fields, the valence change of the metal cations during switching, and much more. In addition, the range of applications of ReRAM will be studied and in particular the fascinating possibility of using ReRAM cells as artificial synapses in novel neuromorphic computers to simulate the functioning of the human brain will be investigated.
Nano technology makes it possible to produce materials and structures on the basis of silicium, whose property of absorption can be adjusted and manipulated. This means one can profit from the properties of ultrathin silicium layers with a thickness of less than 10 billionths of a metre (10 nm), which differ fundamentally from regularly used silicium solar cells due to confinement effects.
In this way it is possible to produce solar cells by the means of vertical stacking of ultra thin layers (see picture), which absorb a much higher proportion of the sunlight spectrum than conventional solar cells based on silicium thick-layer cells with “classical” pn-transition. The higher absorption capacity causes a more effective transformation of sunlight into electrical power and hence a higher electrical terminal voltage at the tandem solar cell. In theory, the amount of irradiated sun energy transformed into electrical power could increase from 44% to 66%. This data shows that the procedure is 2 to 3 times more effective than those which are being currently used.
In the context of the BMBF-cooperative project being carried out at the institute of semiconductor electronics at RWTH Aachen, SINOVA thin silicium layers are integrated into alternative lateral Si-quantum-layers solar cells nano-technology procedures (see picture), which clearly demonstrates the desired increase of electrical output voltage. This forms the foundation of maximum efficiency solar cells in the future.
About 3 million people worldwide suffer from the hereditary eye disease “Retinis Pigmentosa”, which causes the slow destruction of the retina and the desensitisation of the photoreceptors. Although approximately 30% of the nerve cells of the retina remain unaffected, the patient gradually goes blind due to the loss of function of cones and rods. Despite several studies into the area, the disease can neither be cured nor stopped with the help of modern medicine. The application of modern microelectronic and semiconductor technology not only gives “Retinis Pigrmentosa” sufferers back their sight, but also a renewed quality of life.
With the help of specific glasses and eye implants, both developed by departments of the Faculty of Electrical Engineering and Information Technology, blind people are able to see again. There is a camera inside the glasses which converts the pictures taken into digital signals. Two different chips are implanted behind the eye of the blind person, one of which receives the digital signal of the camera and passes it on to a second stimulation chip. This stimulation chip generates minute electric shocks, which are passed on as bipolar impulses to the nerve cells via micro electrodes, which have been implanted into the retina.
Finally, the nerve cells of the retina which are still intact send information to the brain, where it is processed and converted into pictures.