Physical barriers (210) are present between neighbouring pixels (200) on a circuit substrate (100) of an active-matrix display device, such as an electroluminescent display formed with LEDs (25) of organic semiconductor materials. The invention forms at least parts of the barriers (210) with metal or other electrically-conductive material (240) that is insulated (40) from the LEDs but connected to the circuitry (4, 5, 6, 9, 140, 150, 160, T1, T2, Tm, Tg, Ch etc.) within the substrate (100). This conductive barrier material (240) may back up or replace, for example, matrix addressing lines (150) and/or form an additional component either within the pixel array or outside. The additional component comprising the conductive barrier material (240) is advantageously a capacitor (Ch), or an inductor (L) or transformer (W), or even an aerial.