Majlesi Journal of Telecommunication Devices Vol. 6, No. 1, March 2017 5 Two Efficient Approaches for Improving Field Emission Properties of ZnO NRs Marziyeh Advand 1,2 , Bahram Azizolah Ganji *,1 , Mohammadreza Kolahdouz 2 1- Department of Electrical and Computer Engineering, Babol Noshirvani University of Technology, Babol, Iran Email: baganji@nit.ac.ir (Corresponding author) 2- Department of Electrical and Computer Engineering University of Tehran, Tehran, Iran Email: marziyeh.advand@gmail.com Received: January 2017 Revised: January 2017 Accepted: January 2017 ABSTRACT: The structure of pure and Al doped ZnO (AZO) nanorods (NRs) has been studied. A post annealing procedure in oxygen ambience at 400C were used in order to improve crystallinity of both group of samples. The XRD patterns illustrate that the Al doped ZnO NRs were successfully synthesized using our method. Then, the field emission properties of the as grown NRs before and after annealing process were evaluated by our home-made setup. Experimental results show that Al density in ZnO NRs directly affects FE properties of these samples. The oxygen post annealing process leads to a significant improvement in the field emission performances of pristine and doped ZnO NRs including considerably lower turn on voltage, and higher emission current. KEYWORDS: Zinc oxide, Al-doped Zinc Oxide, Nanorods, Field Emission, Oxygen Annealing, Oxygen Vacancy 1. INTRODUCTION Field emission effect plays an important role in high sensitivity gas and pressure sensing[1], flat panel displays[2], [3] and telecommunication devices such as compact microwave amplifiers[4]. In this manner, the understanding of the field emission that occurs in the electronic and communication devices like RF-MEMS switches is a very important issue[5], [6]. Exponential relationship between voltage and current in field emission mechanism results in high-precision measurements[7]. Therefore, it can be used for high accuracy detection of low concentrations gases. The use of field emission method is more attractive for gas sensing because of high-speed amenability and its low power consumption[8]. Turn-on field (  ), threshold field (  ), emission current density, field screening effect and field enhancement factor () are the main factors that determine field emission performance of materials[9]. In this manner, ZnO is a promising candidate for the acutely effective cathode emitters due to its chemical stability and its high device packaging density[10]. In order to achieve an excellent FE performance from ZnO NRs array, the array’s resistance, work function through the energy band binding and the quality of metal contact are important[11]. Therefore, ZnO doping with Aluminum and a post annealing procedure in oxygen ambience can positively affect the FE properties of ZnO nanostructures[12]. This method adjusts internal bandgap of nanostructure and its carrier concentration[12]. In this paper, the morphology of the as grown ZnO arrays were investigated using top view and cross- sectional view FESEM images. The crystalline quality of all the samples was investigated using X-ray diffraction method. Finally, the IV curves and field emission responses were measured by Keithley-K361 parameter analyzer in a vacuum chamber ( Pa) at room temperature to determine the effect of doping process and oxygen annealing on the enhancement of Fermi level and reduction of the work function. 2. MATERIALS AND METHODS In order to investigate the ZnO NRs' field emission properties, different percentages of Al were doped into ZnO NRs. For this purpose,      glass substrates were purified by sonicating in acetone, ethanol, and de-ionized (DI) water. The glass substrates were utilized for strong insolating and the growth of Al-doped NRs. Then, 250 nm layer of titanium and 350 nm-thick layer of gold were consecutively deposited on the purified glass substrate by radio frequency (RF) plasma sputtering. The titanium thin film layer was used as an adhesive layer to improve interfacial bonding between the glass substrate and the gold thin film. After that, 200nm thickness of 2% Aluminum- doped ZnO (AZO) seed layer was deposited on the Au layer by RF sputtering system (Fig.1). In the next step,