Georg Dr Gaertner

Light extraction from OLEDS with (high) index matched glass substrates

In a conventional bottom emitting organic light emitting diode only about half of the generated photons are emitted into the glass substrate (out of which 25% are extracted into air), the other half being wave-guided and dissipated in the OLED stack. This is due to the refractive index mismatch between the organic layers (n=1.7-1.9) and the glass substrate (n=1.5). By matching the refractive index of the substrate (n=1.8) and organic layers and augmenting the distance of the emission zone to the cathode to suppress plasmonic losses light extraction into the substrate can be increased to 80- 90%. This is shown by simulation and experiment. Furthermore the effect of pyramidal structures on the light extraction from the substrate into air is studied by experiment and simulation. Ultimately it is limited by the reflectance of the OLED stack. The experimental results for monochromatic light are well corroborated by simulations. The main conclusion is that most photons can be out-coupled from the organic stack into an index matched substrate. The OLED light extraction problem is thus reduced to an effective extraction from the substrate into air.

Ion bombardment investigations of impregnated cathodes

Ion bombardment is one of the important factors limiting the performance of impregnated cathodes (=Ba dispenser cathodes) in high end television tubes or in colour monitor tubes. Hence, when designing a new gun with, e.g. higher electron beam current density, it is important also to model the influence of ion bombardment. Therefore, relations between basic parameters as a function of temperature need to be known quantitatively. In this paper, the emission slump of impregnated cathodes has been analyzed in a diode configuration in UHV with a differentially pumped Ar ion gun. The emission degeneration during and regeneration periods after ion bombardment have been investigated as function of cathode temperature, ion current and ion energy. One of the important results is, that the degeneration time coefficient is only weakly dependent on ion energy. The data matrix obtained can be used to improve the ion bombardment model applied in new electron gun design.

Technological waves and future perspectives of vacuum electronics

Vacuum electronics (VE) have been one of the motors of industrial growth in the last 130 years. The development of VE concepts has been pushed by several technological waves/cycles, starting with incandescent lamps, continuing with the radio tube era then followed by the cathode ray tubes. Before and during these cycles also the enabling technologies for VE, especially vacuum technology and cathode technology, have been developed further improved continously. Despite the decay of the first 3 waves, vacuum electronics is still alive in the form of microwave tubes, X-ray tubes and other applications. In the case of microwave tubes their specific advantages in the high power/high frequency domain over solid state is discussed. This could open new perspectives for future applications in IC design. In this talk first the different technological waves are described and then the progress of the two main enabling technologies is elucidated, monitored by decreasing vacuum base pressure and increasing cathode emission capabilities. Finally future perspectives for VE are given.

Past, present and future of Vacuum Electronics

For 150 years Vacuum Electronics (VE) have been the motor of technical innovation in several important application areas. They have enabled a lot of basic inventions and have dominated development and industrial growth in their application areas over more than a century. First a description of the development of vacuum tubes with special emphasis on the electron sources from the early days to the modern state of the art [1,2,3] is given. Changing application scopes from radio transmission, microwave generation, X-ray tubes, display tubes, gas lasers, gas discharge lamps and particle accelerators are addressed. Prospects for the future of standard technology are outlined: e.g. high power vacuum electronics (microwave gyrotrons), space applications of VE (long-lived microwave tubes, ion thrusters), thermionic energy converters, e-beam lithography or vacuum based high resolution characterization.

Ba/BaO evaporation measurement during accelerated life test

The Ba and BaO evaporation rates of a thermionic cathode have been measured at 145K and 170K above the typical operating temperature being about 1033K. According to the measurement result, the relationship between cathode lifetime and operation temperature has been discussed. A comparison life test also be done between a poisoned but reactivated cathode and a normal one under the same condition. We found almost the same emission current at the beginning but different current decrease speed and Ba evaporation rate at the course of the life test.