Table 2.
Estimated values for specific components of pixel noise, corresponding to the architectural rules and properties of the various arrays examined in this paper (column 1). Pixel shot noise at 1 fps, σshot (column 5), as determined from Eq. 5 using the measured dark current per pixel at a Vbias of 6 V, Ipix-dk, in column 2. The uncertainty in these shot noise values is approximately ±2.5%, based on an estimated experimental uncertainty of ±5% in the Ipix-dk measurements. Since dark current was not determined for PSI-1, no shot noise value is reported in the table. Thermal noise from the pixel addressing TFT, σthermal (column 6), as determined from Eq. 6 using the photodiode capacitance, CPD, in column 4. CPD was determined from the thickness of the intrinsic layer of the photodiode (dPD in column 3), the area of the photodiode (given by the product of the geometric fill factor of the photodiode, FFgeo (Table 1), and the square of the pixel pitch, apix (Table 1)), assuming a dielectric constant of 12 for a-Si:H. Preamplifier noise, σpreamp (column 7) for hypothetical arrays with 30 cm long data lines populated with pixels having the pixel pitch and properties of the arrays listed in column 1, as determined from Eq. 7.
| Array | Ipix-dk at 6 V (fA∕pixel) | dPD (μm) | CPD (pC) | σshot (e, rms) | σthermal (e, rms) | σpreamp (e, rms) |
|---|---|---|---|---|---|---|
| Pagescan I | 2.50 | 1.40 | 0.51 | 125 | 404 | 2040 |
| Pagescan III | 5.20 | 1.50 | 0.70 | 180 | 470 | 1480 |
| Hawkeye | 0.845 | 1.50 | 0.33 | 73 | 322 | 1420 |
| M10 | 64.3 | 1.50 | 0.99 | 634 | 561 | 2270 |
| M13 | 5.08 | 1.50 | 0.96 | 178 | 553 | 1800 |
| HOFFA | 3.57 | 1.00 | 0.43 | 149 | 369 | 2040 |
| PSI-1 | n∕a | 1.00 | 0.60 | n∕a | 436 | 780 |