On MAPS-On-Diamond sensors and their potential as innovative devices

Synthetic diamond is a very attractive material to build sensors and devices due to its properties as radiation resistance, very low noise, human tissue equivalence. Aside from costs and dimensions, one important drawback is the creation of highly segmented devices. Recently, a new technique, the silicon-on-diamond bonding via laser pulses, has been developed to instrument diamond substrates with pixellated CMOS imagers acting as readout chips to obtain ionizing radiation detectors. This new class of devices could be polarized at the same voltage levels of a standard diamond detector, i.e. 1 V/μm to reach the depletion region. The bias is applied between the diamond side and the silicon side, and it drops almost entirely through the diamond thickness leaving undisturbed the working of the CMOS circuitry. When an e-h pair is created in the diamond, the charges of one type will drift towards the diamond-silicon interface according to the sign of the polarization applied and then collected by the metal electrode on the silicon surface. The collected signal is due both to the charge created in the silicon and to the charge created in the diamond bulk. As CMOS silicon layer, we have used a custom Monolithic Active Pixel Sensors (MAPS) where are implemented both small pixels and low noise electronic circuits. A proof of principle of the bonding of a thinned MAPS and a diamond substrate producing a MAPS-On-Diamond device has been fabricated (no damage to the CMOS circuitry) and is capable of collecting both contributions. We will discuss the present limitation of the produced devices and the possibility of using a commercial CMOS Image Sensor (CIS) as the instrumented layer for the diamond substrate and asses the expected performances in detecting ionizing radiation.