Research Of Compounded Cone Field Emission Arrays

Spindt-type field emission array, which has many advantages such as low working temperature, quick launching speed, good stability, low power consumption and high emission current density is becoming more and more important in many areas like flat panel display, traveling wave tube and sensors, so it has been a research hotspot all over the world since invented.At present the most common tip materials of Spindt-type field emission arrays are molybdenum(Mo) and silicon(Si), but these materials both have high work function and the tips made of them are fragile. Lanthanum hexaboride(LaB6) has a low work function, high melting temperature, stable physical and chemical properties and good resistance to ion bombardment, which makes it an excellent field emission material. However, the cones made of LaB6 are easy to detach from the substrate because of lacking adhesion to the silicon. On the other hand, the shapes of the cones are different with each other due to the inhomogeneity of deposition and the emission current of different cones may vary considerably. So spark phenomenon often occurs when the emission current of some cones is too large, then the tips may be destroyed and it can even cause short circuit between grid and cathode which leads to a failure of the whole array.The main contents include:1. A composite cone structure is designed based on the traditional Spindt-type field emission arrays and previous work of our lab. Firstly we deposit Mo transition steps in the grid holes and then LaB6 tips are deposited on the steps, in this way the properties of these two materials can be combined in order to reduce work function and increase adhesion of the cones. In addition, under each cone we deposit a silicon resistive layer which plays the role of divider resistors, it can make the emission current from different cones more uniform and reduce abnormal emission and spark phenomenon. Besides, the resistive layer can also protect the field emission array in an overcurrent situation and improve the stability of field emission arrays.2. An array of grid holes are made on a silicon substrate through oxidation, photolithography and RIE and some other methods, the diameter and height of each grid hole are both 1μm, the distance between two holes is 5μm and the total area of the array is 1×1mm2. Second, by evaporation coating technique, we deposit a silicon resistive layer, an aluminum sacrificial layer, a Mo transition steps and a LaB6 tip successively in each grid hole. After removing the sacrificial layer with water-bath dilute phosphoric acid, a composite cone field emission array can be obtained.3. Some problems occur during the preparation process of field emission arrays, such as cracking of films, shedding of cones, oxidation of material and the burrs on the surface of cones. And a series of work is tried to deal with the problems, including annealing, hydrogenation and Aging process. As a result it can be seen that the problems are solved and the performance of the field emission array are enhanced.4. The field emission arrays are tested for their performance and stability. As a result, the maximum emission current of the device reaches 8mA and the current density surpasses 0.8A/cm2 under the voltage of 180 V. Besides, the field emission of the device is relatively stable so the preparation process of the composite cone array structure is proved to be feasible and effective.