The TopmetalSe-MPW6 is a prototype charge sensing detector for the Selena Neutrino Experiment submitted to the OpenMPW 6 run. It is based on the Topmetal-II ^- Active Pixel Sensor, which we had previously characterized. A Topmetal pixel contains an electrode made from the topmost metal layer, surrounded by a guard ring (gring). Each pixel is directly coupled to a charge sensitive amplifier (CSA), which converts input charge to an analog signal. The TopmetalSe-MPW6 contains 2 100x100 pixel array test structures in each user area. The pixels have a square geometry, with a 10.2 µm electrode with and a 15 µm pixel pitch. The simulated noise is ~15 electrons with a charge conserion gain of ~25 µV per electron.

The TopmetalSe will be implemented in the final detector design of the Selena neutrino experiment, which couples an amorphous selenium (aSe) ionization target to a CMOS pixel array as an imaging detector for next generation neutrino physics. The physics is detailed in the White Paper here. In a nutshell, by coupling CMOS charge sensors directly to aSe, one can image electron tracks as they move through the detector. By measuing the energy, track geometry and timing of these electrons, we can look for unique nuclear decay patterns to probe the nature of neutrinos.

For the final design, the TopmetalSe will require an opening in the passivation layer in order to directly couple to aSe. But for the OpenMPW 6 run, we are unable to do so, and thus, this submission will be used as a test of the design and workflow. The stray capcitance between the surrounding gring and the electrode will allow us to inject charge and characterize the pixel performance in the absence of an external ionizaiton source.