1. A product-sum operation circuit element comprising: an insulator substrate; at least one single crystal semiconductor thin film region on the insulator substrate, the at least one single crystal semiconductor thin film region extending in a first direction; a ferroelectric thin film deposited on the insulator substrate for covering at least the at least one single crystal semiconductor thin film region; and an electrode, formed on the ferroelectric thin film, the electrode extending in a second direction and crossing the at least one single crystal semiconductor thin film region; wherein the at least one single crystal semiconductor thin film region includes first, second and third semiconductor thin film sections; wherein the first and third sections are of a same conductivity-type and the second section is of a conductivity-type which is the opposite of the conductivity-type of the first and third sections; and wherein the first, second and third semiconductor thin film sections are arranged along the second direction with the second section disposed between the first and third sections.