Radiation Hardness Studies of Monolithic Active Pixel Sensors ...

30 KAPITEL 3. STRAHLENSCHÄDEN
214 Measurements of the Prototype Pixel Devices
hypothesis is based on a lack of n-well guard-rings around the test structures. These rings are
present in the case of the main detecting arrays and they cut current paths from outside of
the active volume.
Abbildung 3.7: Leckstrom als Funktion der Temperatur a) vor der Bestrahlung, b) nach der Bestrahlung,
c) nach drei Wochen Lagerung bei Raumtemperatur und d) nach einem 24-stündigen
Ausheizen des Chips bei einer Temperatur von 100 ◦C. Der Plot wurde [Dep02] entnommen.
Figure 6-37: Variation of the leakage current related to a single nwell/p-epi
diode (STANDARD and NPOL_FL) as a temperature
function measured on MIMOSA III test structures (a) before
irradiation and after 10 keV photons irradiations; (b) one day after, (c)
3 weeks of room temperature annealing, and (d) after additional 24
hours annealing at 100 °C.
The second hypothetic reason, explaining the excess of the measured leakage current can be
the modification of the test structures layout with respect to the actual pixels. The space
occupied by the transistors was liberated and filled with a p + -type region and the test
structures including their vicinity were not masked against filling with an n + -type region and
poly-silicon * . Only the surface of the main detecting arrays was protected against filling. The
filling is done automatically by foundry over the unprotected regions in order to satisfy filling
ratios for each layer according to the DRC † rules. The created floating n + -type and poly-