Imager devices have a sensor array and a peripheral region at least partially surrounding the sensor array. At least one transistor in the peripheral region has a gate stack sidewall spacer that differs in composition from a gate stack sidewall spacer on at least one transistor in the sensor array. Imaging systems include such an imager device configured to communicate electrically with at least one electronic signal processor and at least one memory storage device. Methods of forming such imager devices include providing layers of oxide and nitride materials over transistors on a workpiece, and using etching processes to form gate stack sidewall spacers on the transistors.