Jay Lewis

Thin-film permeation-barrier technology for flexible organic light-emitting devices

One of the advantages of organic light-emitting devices (OLEDs) over other display technologies is the ability to fabricate them on flexible substrates. As polymer substrates do not offer the same barrier performance as glass, OLEDs on polymer substrates will require thin-film barriers on both the bottom and top side of the device layers for sufficient lifetimes. This article provides a review of permeation-barrier technologies as well as the current status of thin-film permeation barriers for OLEDs. Topics include the implications of various device structures, permeation rate measurement, background and state-of-the-art of barrier technology, and mechanical and optical considerations for effective barriers.

Highly flexible transparent electrodes for organic light-emitting diode-based displays

Multilayer indium-tin-oxide (ITO)–Ag–ITO stacks were evaluated as transparent conductors for flexible organic light-emitting diode (OLED) displays. The ITO–metal–ITO (IMI) samples exhibited significantly reduced sheet resistance over ITO and greater than 80% optical transmission. The IMI films deposited on plastic substrates showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. OLEDs were fabricated on both ITO and IMI anodes, and the devices with IMI anodes showed improved performance at current densities greater than 1mA∕cm2 due to the improved conductivity of the anode.

Superlattice-based thin-film thermoelectric modules with high cooling fluxes

In present-day high-performance electronic components, the generated heat loads result in unacceptably high junction temperatures and reduced component lifetimes. Thermoelectric modules can, in principle, enhance heat removal and reduce the temperatures of such electronic devices. However, state-of-the-art bulk thermoelectric modules have a maximum cooling flux qmax of only about 10 W cm−2, while state-of-the art commercial thin-film modules have a qmax <100 W cm−2. Such flux values are insufficient for thermal management of modern high-power devices. Here we show that cooling fluxes of 258 W cm−2 can be achieved in thin-film Bi2Te3-based superlattice thermoelectric modules. These devices utilize a p-type Sb2Te3/Bi2Te3 superlattice and n-type δ-doped Bi2Te3−xSex, both of which are grown heteroepitaxially using metalorganic chemical vapour deposition. We anticipate that the demonstration of these high-cooling-flux modules will have far-reaching impacts in diverse applications, such as advanced computer processors, radio-frequency power devices, quantum cascade lasers and DNA micro-arrays.

Thermal management of ultra intense hot spots with two-phase multi-microchannels and embedded thermoelectric cooling

This study concerns cooling of electronic components of intense background heat flux with one ultra intense hot spot (e.g. 1000 Wcm−2 on a footprint of 1 cm × 1 cm with 5000 Wcm−2 applied to a 0.02 cm × 0.02 cm region at the center). To manage these extreme heat fluxes and consequently surpass the thermal-hydrodynamic challenges and design paradigms, for example as specified in a recent DARPA request for proposals (Intrachip/Interchip Enhanced Cooling Fundamentals - ICECool Fundamentals [1]), on-chip two-phase multi-microchannel cooling integrated with a superlattice (SL) thin-film thermoeletric cooling (TEC) technology was investigated via computer simulations.The simulations showed that increasing TEC electrical current results in greater enhancement of heat flow through the TEC, but at high currents this benefit is offset by a net addition of heat to the system, which must also be evacuated by the microchannels. When optimized, a minimum peak junction temperature of about 86 °C for a current of about 8 A was found, which represented a reduction of about 4 °C from a maximum allowed 90 °C at the ultra-intense hot-spot, thus potentially significantly capable of exceeding the DARPA [1] requirement, due to the embedded SL TEC within the microevaporator (ME) structure.Copyright

Mechanical evaluation of permeation barriers for flexible OLED displays

Mechanical flexing of plastic substrates coated with thin film permeation barriers causes sub-micron cracks that lead to device degradation. We demonstrate an improved method to rapidly observe cracks and evaluate mechanical performance of permeation barriers.