Low noise floating-diffusion amplifiers, made in double and single layer membrane poly-Si technology, are characterized including scaling rules for the 1/f noise, thermal noise, 3 dB bandwidth and conversion gain. A comparison is made between buried-and surface-channel detection node transistors for various channel widths, lengths, and bias currents. A new method for measuring the total detection node capacitance is used. The results are modeled using a noise model that includes shot noise from hot-electron effects.