A new cold cathode using pulsed laser deposited lanthanum monosulfide thin films

Using MEMS technology, an array of cold cathodes was fabricated by pulsed laser deposition (PLD) of chemically and thermally stable lanthanum monosulfide (LaS) thin film anode and cathode contacts. The latter were defined via etching and processing of two different pieces of (100) Si wafers separated via a highly resistive sputter deposited aluminum nitride (AlN) layer whose thickness was used to control the anode to cathode spacing. The top and bottom Si wafers were aligned and glued together using high temperature, vacuum compatible epoxy. Field emission (FE) characteristics were recorded in a vacuum chamber with a base pressure near 10^-7 Torr. An average electric field threshold for Fowler-Nordheim (FN) field emission in the range of 100 V/mum was measured. A maximum current density of 8 mA/ cm² was recorded which is large enough for flat panel display applications. The largest emission current measured was about 5X10^-7 A above which thermal runaway occurred leading to a failure of the cathode. The failure mechanism is most likely due to Joule heating in the aluminum (Al) thin film underneath the LaS cathodes.