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Research Activities
Device Physics



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  Device Physics        
To internal topic Technology        
  Though our technology has its origin in microelectronics our fabrication process differs substantially from microelectronics standards. Purity reasons, the demand for a fully doublesided process as well as large detector surfaces are the main causes making our fabrication process neither adaptable nor directly transferable into a conventional microelectronics process unit. We are in the unique position to have a production line which combines processes for ultra-pure silicon wafers with the small-scale technology of very large system integration (VLSI) electronics. Except ion implantation which is outsourced to service providers, processing is done exclusively in our 1,000 square meter cleanroom. A variety of technology key features distinguishes the MPG HLL from microelectronics fabrication.     
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  Photo of wafer boats containing wafers to be inserted into a MPG HLL furnace.    
To internal topic Design & Simulation        

The development of new detector concepts requires a deep insight into device physics and technology. The new device ideas have to undergo a thorough examination through detailed simulations of the fabrication process as well as the electrical behaviour before becoming structures in silicon. A profound detector simulation is mandatory to reduce the number of fabrication cycles until the final application in an experiment. All silicon detectors invented, designed, fabricated and tested at the MPG HLL are optimized by means of two and three dimensional device and process simulation.
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Simulation image of three-dimensional electron density distribution within a rectangular DEPFET after signal electrons collection.    
To internal topic Electronics        
The need for bigger and faster multi channel X-ray detectors generates ever growing amounts of data. Deploying modern integrated electronics is required to build an adequate data acquisition system. It has to control the detector, to process analog data, to convert the analog signals into digital values and store data in computer memory. Algorithms are working on raw data and generating real images and spectra.   Photo of a field programmable gate array (FPGA) used in our DEPFET data acquisiton system.


  A challenging part of data acquisition is the extraction of an information signal from a noisy detector output which is usually carried out by analog filtering stages integrated in one silicon chip. To combine the various components of electronics sophisticated printed circuit boards and delicate mountings are necessary. We improve our detector developments by the design of readout electronics. In cooperation with partners the MPG HLL integrates complex working detector systems.
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  Within these areas there are the following research topics:        
PDF document  Silicon Strip Detectors        
  Silicon strip detectors were the first devices using the lithographic capabilities of microelectronics to produce a detector with high position resolution. A strip detector is an arrangement of strip like shaped implants acting as charge collecting electrodes. Placed on a low doped fully depleted silicon wafer these implants form a one-dimensional array of diodes. By connecting each of the metalized strips to a charge sensitive amplifier a position sensitive detector is built.   Schmeatic view of the operation principle of a double sided strip detector
  Two dimensional position measurements can be achieved by applying an additional strip like doping on the wafer backside by use of a double sided technology.
[more... PDF document PDF 151kB]
PDF document  Silicon Drift Detectors – made by MPG HLL  
  The development of Silicon Drift Detectors (SDDs) was one of the first activities in the MPG HLL. E. Gatti and P. Rehak were visiting the MPG für Physik just after their invention and inspired the local researchers. But it took about 15 years after the first publications until the first units were getting an industrial product.   Schematic view of a cylindrical silicon drift detector with an integrated JFET as a first amplifier  
  Silicon drift detectors have been used in many scientific fields: astrophysics, high energy physics, material research, medicine, synchrotron radiation research and solid state physics – to mention a few. In addition to their use in basic research, SDDs are offered as spectrometers for industrial applications.
[more... PDF document PDF 268 kB]

PDF document  pnCCD Detectors        
  The pnCCDs have been developed for the precise detection of photons, the visible and near infrared light, UV light, and X-rays as well as particles, such as minimum ionizing particles, electrons, protons, Alpha particles etc. pnCCDs measure the arrival time of the radiation with a precision of milliseconds, the energy of X-rays and particles with a precision of approximately 100 eV, if fully stopped in the silicon and their position within a range of a few micrometers.   Schematic CCD structure as seen from inside an CCD  
  Typical pnCCD detectors have responsive surfaces of the order of 10 cm². The sensitive volume can be as thick as 1 mm, allowing for an efficient detection of X-rays up to 50 keV.
[more... PDF document PDF 189 kB]
PDF document  DEPFET Active Pixel Sensors        
  Being the most consequent application of the principle of sideward depletion, the combined detector-amplifier structure DEPFET is one of the most advanced concepts in the MPG HLL portfolio. DEPFET structures can be used as building blocks for a large variety of different devices ranging from optical photon sensors to X-ray imagers and particle trackers. Due to their extremely low detector capacitance they exhibit excellent signal-to-noise ratio and energy resolution. Currently, DEPFET based active pixel detectors are developed for X-ray astronomy, planetology and particle physics.
[more... PDF document PDF 218 kB]
  Schematic vertical section of a circular DEPFET pixel cell for XEUS  
PDF document  Avalanche Amplifying Devices        
  Arrays of avalanche photo diodes operated in Geiger mode are forming so called Silicon Photomultiplier (SiPM). MPG HLL is developing SiPMs in which the fill factor of those devices is maximized as the passive components needed for the successful operation of those devices are placed in the bulk underneath the sensitive region - SiMPl concept.
  simpl scheme  

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