We proposed a novel defect-controlled tunneling cathode using ion-beam modified polyimide film as a tunneling insulator. Our aim is to achieve high efficiency electron emission by means of hot electrons generated by passage through defects in the ion-beam modified polyimide film. The emission characteristics and energy distribution of emitted electrons were measured with a triode configuration. The material was spin-coated and then irradiated with Ar ions to modify its electrical characteristics. The cathode was fabricated with a conventional thin film process. Current-voltage characteristics of the cathode and the energy distribution of emitted electrons were investigated. Electron emission took place upon the application of electrical stress that decreased the gate current by three orders of magnitude, a phenomenon that is called forming. After forming, a threshold voltage of about 30 V and emission efficiency of 7% at 70 V with a relatively uniform spatial distribution was achieved. The peak of energy distribution of emitted electrons was raised when the applied gate voltage was increased. The electron energy distribution analysis clearly shows that hot electrons generated in the cathode are emitted in vacuum. (C) 2004 American Vacuum Society.