Metal Gate Recessed Access Device (RAD) for DRAM Scaling
A functional DRAM with higher data retention characteristics than a planar access device has been demonstrated, using a metal gate recessed access device (RAD). Chemical vapor deposition (CVD) and atomic layer deposition (ALD) were used to deposit titanium nitride (TiN) and tantalum nitride (TaN), respectively. CVD TiN and ALD TaN-CVD TiN laminate gate stacks were integrated with a RAD module. ALD TaN-CVD TiN laminate gates showed enhanced drive current (IDS), higher transconductance (GM), higher mobility (¿EFF) and reduced off current (IOFF) characteristics compared to CVD TiN gates. Device characteristics and reliability data for both the planar devices and RADs are presented. The ALD TaN-CVD TiN laminate metal gate RAD showed much improved data retention characteristics compared to a conventional planar device with a poly silicon gate. The optimum thickness of ALD TaN in the laminate stack is discussed.
On the thermal stability of atomic layer deposited TiN as gate electrode in MOS devices
The work function of ALD TiN was found to be above 5 eV after RTP annealing below 800/spl deg/C in a nitrogen atmosphere, while higher annealing temperatures cause a drop in work function by about 0.3-0.5 eV. The effect was found for TiN metal gates on both SiO/sub 2/ and Al/sub 2/O/sub 3/ gate dielectrics in MOS-capacitors and was seen in C-V as well as in I-V measurements. On the contrary, annealing of SiO/sub 2/ capacitors in oxygen-enriched N/sub 2/ atmosphere increased the work function. A variation in EOT of less than 2 A was demonstrated for the various annealing temperatures, concluding that the ALD TiN is stable in contact with the different dielectric materials. However, the decrease in work function that is found in this investigation may implicate that ALD TiN is less suitable as a metal gate for pMOSFETs.
Compressive and flexural properties of hemp fiber reinforced concrete
The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.