K. Shanmugasundaram

Mist fabrication of light emitting diodes with colloidal nanocrystal quantum dots

In this letter, we report a mist-deposition process for the assembly and patterning of nanocrystal quantum dots (NQDs) during the fabrication of quantum dot light emitting diodes (QD-LEDs), which allows for tight controls over the thickness, surface morphology, composition, and resolution of NQD emissive layers. A defect-free featuring uniform brightness QD-LED containing a mist-deposited emissive CdSe(ZnS) NQD layer was demonstrated. Additionally, the technique of successive mist deposition of multicolor NQDs through a set of registered shallow masks was employed to create a 6×6 matrix of alternating pixels composed of 5nm diameter CdSe(ZnS) NQDs (green) and 8nm diameter CdSe(ZnS) NQDs (red) on the same substrate. The results obtained demonstrate the potential of mist-deposition technology in the future development of full-color QD-LED displays.

Studies of mist deposition for the formation of quantum dot CdSe films

Films of CdSe(ZnS) colloidal nanocrystalline quantum dots (NQDs) were deposited on bare silicon, glass and polymer coated silicon using mist deposition. This effort is a part of an exploratory investigation in which this deposition technique is studied for the first time as a method to form semiconductor NQD films. The process parameters, including deposition time, solution concentration and electric field, were varied to change the thickness of the deposited film. Blanket films and films deposited through a shadow mask were created to investigate the methods ability to pattern films during the deposition process. The differences between these deposition modes in terms of film morphology were observed. Overall, the results show that mist deposition of quantum dots is a viable method for creating thin, patterned quantum dot films using colloidal solution as the precursor. It is concluded that this technique shows very good promise for quantum dot (light emitting diode, LED) fabrication.

Deep lateral anhydrous HF/methanol etching for MEMS release processes

As demonstrated earlier, gas-phase etching of sacrificial oxide with a vapor mixture of anhydrous HF (AHF) and methanol (CH3OH) offers a clean, stiction-free, effective etching technique for microelectromechanical systems (MEMS) release. The use of AHF/methanol process in MEMS release operations is explored in the deep lateral etching of patterned silicon-on-insulator (SOI) substrates using a 200 mm multiwafer commercial module, which assures adequate process throughput. It was determined that highly selective, with respect to both Si and Si3N4, etching of SiO2 can be accomplished by controlling pressure and wafer temperature. It was also observed that the vertical etch rates for both the AHF/methanol and the HF: H2O solution was higher than the rates of lateral etches in confined geometries. Furthermore, the AHF/methanol and 1:10 HF: H2O etch chemistries were directly compared in releasing silicon cantilevers up to 500 µm in length and a significantly faster, stiction-free process was observed in the former case. Adequate process reproducibility from wafer to wafer as well uniformity across the wafer was demonstrated.

Current Advances in Anhydrous HF/Organic Solvent Processing of Semiconductor Surfaces

The process in which anhydrous HF (AHF) is mixed with the vapor of an organic solvent for the purpose of etching of native SiO2 on Si surfaces is well established (e.g [1-4]). The process was also explored as part of a dry-wet wafer cleaning sequence [5]. More recently, the same process has been successfully expanded into MEMS technology for the purpose of stiction-free releasing of structures by isotropic etching of sacrificial SiO2 [6,7]. The current strong push in advanced Si digital IC technology toward extremely fragile 3D geometries engraved on Si wafer surfaces, in which case conventional etch methods may not work properly [8], as well as needs with regard to native oxide etching in emerging Si-based technologies such as solar cell manufacturing has brought about renewed interest in AHF technology.