Memory characteristics of MNNOS capacitors with various energy band gaps of silicon nitride

A thin-film transistor-type nonvolatile memory device with a nitride-nitride-oxide (NNO) stack structure was fabricated. The silicon-nitride layers for blocking and charge storage were deposited at low temperatures by employing ICP-CVD. The optical band gap energies of the silicon nitride were between 2.8 eV and 5.8 eV. We used silicon nitride with optical band gap energies of 2.8 eV and 5.8 eV for the charge storage layer and the blocking layer, respectively. The thin tunneling layer formed by silicon-oxynitride was only grown via a nitrous-oxide plasma. The characteristics of the NNO stack structure showed a very large memory window. We successfully obtained a memory window of 24 V with a bias voltage swing between -20 V and +20 V. A large capacitance-voltage hysteresis was obtained, which was probably a result of the electrons and the holes trapped at deep trap levels and of the band gap offset. Low temperature fabrication enables the memory device to be applied to poly-Si TFT for display technology.