Surface disinfection has taken on a new role in the context of the corona pandemic. UVC modules based on LED chips strive to replace mercury vapor lamps. However this will only be achieved if the necessary optical performance for disinfection can be guaranteed. We would like to present the development of potting materials for UVC LED chips. The aim was to find a potting material for use at a wavelength of 250 nm, which is sufficiently transparent, easy to process and which remains stable in its properties for many 100 hours at these wavelengths. Furthermore, the total reflection in the LED base body should be minimized by a refractive index of the cured material n >> 1.4. In addition to the aspects of material development, metrological requirements and long-term studies are also presented. We have succeeded in developing a potting technology that can greatly increase the performance of the UVC LEDs by up to 70%.
Deep ultraviolet (UV) light emitting diodes (LEDs) have a wide range of applications such as water treatment, medical diagnostics, sterilization of medical devices and gas measurement. Depending on the desired application, the emission characteristics of UV light must be optimized. In addition to improving the external quantum efficiency, the radiation properties of the UV LED chip can be influenced and supported by the performance of the housing and the assembly technology.
We will present some results on how to improve the optical performance of UV LED chips through optically UV-transparent materials, which are complemented by some basic aging studies. Furthermore, the influence of differently shaped lenses in combination with and without an integrated aluminum reflector is presented.
We want to show the influence of the different optical and thermal elements individually and in combination to show the possibilities to design the optimal radiator module with the desired properties.
For miniaturized optical fiber coupled MOEMS systems, fiber coupling on chip level is necessary. Therefore a silicon chip based optical fiber coupling with high position accuracy is introduced. In this paper, we present the fiber chip coupling on two examples: A superconducting single photon detector (SSPD) and a miniaturized fiber Bragg grating sensor. In case of the SSPD position accuracy between SSPD and optical fiber of ± 1 μm is necessary.
In this paper we show the developed alignment system and the proof of the position accuracy on silicon test chips. Further, we show first experiments of a fiber coupled superconducting test structure in a closed cycle cryostat with regard to stability of the chip stack and thermal connectivity to the cryostat.
The fiber coupling of the fiber Bragg grating sensor is used to miniaturize the sensor overall construction. The fiber Bragg sensor consists of two stacked Silicon photodiodes. The top photodiode is fabricated in a cavity within a remaining 50 μm Silicon membrane and therefore detects only the shorter wavelength range. The bottom photodiode detects the transmitted longer wavelengths. The fiber coupling chip is mounted on top of the photodiode stack. This leads to a compact chip stack with included fiber coupling, without the need for large fiber connectors or ferrule holders. Further, we demonstrate the mounting of the fiber Bragg sensor on a flexible PCB and its performance.
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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