This makes sense for chips that integrate sensing and processing on the same chip. The military tends to need things like that. LIDAR sensors need both sensing

This makes sense for chips that integrate sensing and processing on the same chip. The military tends to need things like that. LIDAR sensors need both sensing and fast counting, which often use different semiconductor technologies. The first flash LIDAR chips had an InGaAs sensor chip and a CMOS counting chip, both ball grid arrays, soldered back to back. If different technology layers on the same chip can do the job, that would simplify the parts.