A key competence of the NaMLab team is the electrical characterization of microelectronic devices for various applications. High performance transistors are investigated with respect to their performance and basic device properties such as mobility and transfer characteristics. Capacitors are evaluated for different applications in the semiconductor industry. In addition, ferroelectric devices, including capacitors and transistors, are studied to determine their memory characteristics and parameters such as polarization, reliability, retention, imprint and fatigue. In depth methods are available to characterize the oxide charges, positions and densities as well as capacitance and leakage mechanisms. State-of-the-art methods incorporating high-k bias temperature stress, fast time dependent break-down, dielectric relaxation and stress induced leakage current have been established to analyze the reliability of devices. The results are employed to predict the device lifetimes. Electrical characterization of microelectronic devices is also possible at very low temperatures and over a very broad voltage range enabling investigations for automotive and energy switching applications.
Hi k MIM capacitors
Carbon based devices
Several problems arise when nano-electronic devices are reduced down to below 10nm. The gate can no longer effectively close the channel (short channel effect) and doping in both the gate and the statistical variation in the number of dopant atoms in the channel and gate electrodes have a significant impact on the device-to-device variations. Further, the performance of the connections to the device and the speed of the channel become more important. For this reason we are investigating the application of carbon materials to the various device components . In particular, pyrolytic graphite for (a) Schottky barrier free source and drain contacts to carbon nanotube (CNT) and graphene channel materials, (b) high-performance mid-band-gap gate electrodes, and (c) Schottky diodes and contacts to silicon.
Fig. 5: Carbon electrodes on a silicon substrate structured with e-beam lithography and etched with an oxygen plasma:
top: SEM picture – bottom: side view of capacitor stack
Carbon nanotubes exhibit a number of exciting properties for semiconductor applications. The nanotubes can be either metallic, with applications for interconnects or gate electrodes, or semiconducting, with uses as transistor channel material. The band-gap of carbon nanotubes can be in excess of 1 eV, comparable to silicon, making low-power, room temperature nano-electronic devices possible. We are looking into the possibility to produce carbon nanotubes in a structured way for device applications .
Fig. 6: Multi-walled carbon nanotubes grown in lithographically defined blocks on a silicon substrate
In its simplest form a photodiode consists of a semiconducting p-n-junction, which is operated under reverse bias. An electrical current is generated by incident light in the junction through the photo-electron effect if the photon energy exceeds the band-gap of the semiconductor material. Typically the current generated is integrated over time and the collected charge is then coded into a brightness value by means of read-out circuits. This kind of photo-detector can be designed to detect visible, infrared, ultraviolet or even soft X-ray light. The Namlab development scope consists of three parts. First, the improvement of the color resolution for photo-sensors by means of alternative, optically active filter layers or novel concepts for the color selection within the photo-active device structure. Progress in this field will reduce the cost for chip manufacturing or extend the color space that can be represented. Second, minimizing the interaction of neighboring photo-diodes by innovative isolation concepts which reduce the electrical and optical cross-talk. Solutions in this area open the route for cell arrays with smaller cell size and reduced pixel artifacts. Finally, novel designs for cell signal read-out and intelligent circuits for post-measurement data processing are being developed in co-operation with the electrical engineering department at the TU Dresden (Prof. R. Schüffny).