Miniaturized versions of nowadays tabletop setups will be necessary for a successful commercialization of quantum cryptography and computing. Within this contribution, we present a concept for downsizing the Hanbury Brown-Twiss configuration. The design is based on optical simulations, with the aim of finding the best compromise of detection efficiency and level of miniaturization. Since scattering effects are important for evaluating the system’s performance, a complete scattering analysis got performed.
Deep ultraviolet (UV) light emitting diodes (LEDs) have a wide range of applications such as water treatment, medical diagnostics, medical device sterilization and gas sensing. The internal quantum efficiency of UVB and UVC LEDs is extremely low. Added to this is the high refractive index of the sapphire substrate. The electrical input power is converted to more than 95% to heat. Typically, ceramic packages of alumina with metal core or aluminum nitride are used. These promise a minimized thermal resistance. Comparative thermal simulations show that even Si with slightly lower thermal conductivity of 150 W / mK compared to aluminum nitride with 180 to 200 W / mK does not necessarily impair thermal management. From the thermal and optical calculations, basic information was extracted that forms the basis of the Si package layout. The advantage of the Si packing due to the possibility of integrating functional components has been worked out. An optimized Si package is presented that meets in particular the requirements of the assembly and packaging technology of UVB and UVC LEDs. The process technology was designed and implemented. The first samples with integrated protection diode, an optimized reflector and an optically adjusted single Fresnel lens are presented. The Si packages are designed for the flip-chip technology of UV LEDs with SnAg soldering, thermo-compression or thermosonic bonding and silver sintering. Furthermore, an outlook is given on the possibilities of an encapsulating technology to improve the light extraction.
UV LEDs are usually mounted in flip-chip technology by soldering or thermocompression bonding to allow the UV light to be emitted through the sapphire substrate. The thermal conductivity of solders is considerably smaller than that of the typical metals used for packaging such as Cu, Ag or Au. For thermosonic- or thermocompression bonding pure metals can be used, however, the contact area is reduced in comparison to soldered contacts. Thermal simulations with different ratios of the number and size of stud bumps to the total area illustrate the direct influence of these parameters on the thermal resistance. The deformation during the bonding process as a function of the processing temperature and the applied force is discussed together with the influence of preprocessing, e.g. coining. Approaches are presented to increase the bonding area to 70 % of the total pad area of the chip. The improvements in the thermal resistance are demonstrated by lock-in-thermography and SEM investigations.
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