as a signal charge read switch alternatively a tft having ldd structures on the high and low potential sides in which the ldd length is larger on the high potential side than the low potential side like the one shown in fig2 may be used for tft 1 formed as a signal charge read switch a tft having an ldd structure on only the high potential side or a tft having ldd structures on both the high and low potential sides may be used for tft 2 formed as a protective diode similar to tft 1 instead a tft having ldd regions on the high and low potential sides in which the ldd length is larger on the high potential side may be used the tft array shown in fig1 and 2 comprises not only tft 1 serving as a signal charge read switch but also tft 2 serving as a protective diode however tft 2 need not always be formed fig2 shows the planar structure of the tft array in this case and fig2 shows the circuit arrangement of one pixel similar to the tft array shown in fig1 tft 1 is formed as a signal charge read switch has a source and drain connected between the node nd 1 connected to one end pixel electrode of the pixel capacitor cs and the signal line s 1 and a gate connected to the scanning line g 1 and is on off controlled by the scanning line g 1 this device has one tft 1 per pixel as described above to increase the pixel opening ratio and reduce the off current a tft having an ldd structure on only the high potential side.