Vertex detector for BELLE II
Thinning technology
Fig. 4: Mechanical model of a Belle II half module. The
reflective surface is the back of the thinned to 50 microns
(top) wafers.
Most of the tracks in Belle II have a slight impulse and the resolution is restricted by multiple scattering. The high S / N of the DEPFET allows the use of very thin detector material, reducing the uncertainty to the resolution is significantly reduced. With our thinning technology, which connect to that of wafers (wafer bonding) and deep anisotropic etching based, we can make self-supporting sensors with a thickness of 75 µm. The entire radiation length of a Belle II module (including control chips, readout and holder) be less than 0.2% of the radiation length.
A module is based on the diameter of a wafer, loadedwith DEPFET pixels. The sensor is thinned to 75 µmouter frame made of thicker silicon ensures that mechanical stability. Find on the sturdy frame control and readout chips space. Two modules are made using etched cutouts and ceramic pins connected to a common module ("Ladder").
Fig. 5: Each Belle II module has 250x800 pixels. For one
readout time of 20 µs, 4 pixel lines are parallel
read out with 100 ns per line.
Two half modules become one module ("ladder")
connected. 8 ladders with 90 mm active length with 1.4 cm
radius for the inner layer, 12 ladders with a length of
128 mm are attached at 2.2 cm radius.