Effects of Composition on the Memory Characteristics of (HfO2)x(Al2O3)1-xBased Charge Trap Nonvolatile Memory

Abstract

According to the 2012 International Technology Roadmap for Semiconductors (ITRS) [1], the conventional floating gate nonvolatile semiconductor memories (FG-NVSM) are approaching their scaling limitation; moreover, new materials and technology are required in order to explore the novel solid state nonvolatile memory device with the desired characteristics, such as the low-cost, high-density and a fast program/erase (P/E) speed for use in mobile electronics [2-5]. For conventional FG-NVSM devices, the charges are stored in a conducting poly-silicon gate, and a single defect in the tunneling layer can discharge the whole memory due to the scaling thickness of the tunneling layer. Based on the concept, that charges are stored in discrete traps within the charge trapping layer, silicon-oxide-nitrideoxide-silicon (SONOS) charge trap flash (CTF) memories with nitride (Si3N4), as the charge trapping layer, have attracted much attention for commercial applications in order to replace the conventional FG-NVSM devices due to lower operating voltage, excellent endurance, smaller size and compatibility with standard CMOS technology [6]. However, one problem in the SONOS memory device is the small conduction band offset between the Si3N4 and the tunneling layer [7], which leads to poor retention characteristics. In order to solve the problem, employing high-k dielectrics, as the charge trapping layer in the SONOS structure, has been reported by many researchers [8-14]. The charge memory structure with a pure HfO2 charge trapping layer demonCharge trap flash memory capacitors incorporating (HfO2)x(Al2O3)1-x film, as the charge trapping layer, were fabricated. The effects of the charge trapping layer composition on the memory characteristics were investigated. It is found that the memory window and charge retention performance can be improved by adding Al atoms into pure HfO2; further, the memory capacitor with a (HfO2)0.9(Al2O3)0.1 charge trapping layer exhibits optimized memory characteristics even at high temperatures. The results should be attributed to the large band offsets and minimum trap energy levels. Therefore, the (HfO2)0.9(Al2O3)0.1 charge trapping layer may be useful in future nonvolatile flash memory device application.