Non-volatile 'flash' memories are key components of integrated circuits because they retain their data when power is interrupted. Despite their great commercial success, the semiconductor industry is searching for alternative non-volatile memories with improved performance and better opportunities for scaling down the size of memory cells. Here we demonstrate the feasibility of a new semiconductor memory concept. The individual memory cell is based on a narrow line of phase-change material. By sending low-power current pulses through the line, the phase-change material can be programmed reversibly between two distinguishable resistive states on a timescale of nanoseconds. Reducing the dimensions of the phase-change line to the nanometre scale improves the performance in terms of speed and power consumption. These advantages are achieved by the use of a doped-SbTe phase-change material. The simplicity of the concept promises that integration into a logic complementary metal oxide semiconductor (CMOS) process flow might be possible with only a few additional lithographic steps.

Electrical conductivity relaxation experiments were performed on thin specimens of Lai_rSrFe0a_, (x =0.1, 0.4) at oxygen partial pressures Po, = 10 -1 bar in the temperature range 923 to 1223 K. The transient response of the electrical conductivity after a sudden change of the ambient oxygen partial pressure was analyzed in the frequency domain. The latter procedure allowed diffusion-limited and surface exchange-limited kinetics of re-equilibration to be distinguished. The response of specimens with thiçknesses of 350 to 460 p.m indicated diffusion-controlled kinetics at Po,> 0.03 bar. The chemical diffusion coefficients, D, were found invariant with oxygen pressure. At 1073 K the absolute values were D = 6.5 x 10-6 cm2 -i for x = 0.1 and D = 1.1 X 10 cm2 s1 for x = 0.4, with activation energies of about 80 kJ/mol. The equilibration process was governed by surface exchange at Po, < 0.01 bar. The surface exchange coefficient, k0, was proportional to pa,, where n = 0.65 to 0.85. This pressure dependency was interpreted in terms of a slow surface process involving an oxygen molecule and a surface oxygen vacancy, and causes the observed sharp transition from diffusion-to exchange-controlled kinetics. The activation energy of k0 was estimated at 110 to 135 kJ/mol.

The influence of phase-change material composition on amorphous phase stability, crystallization rate, nucleation probability, optical constants and media noise is reported for materials with a growth dominated crystallization mechanism. Two material classes have been studied, doped Sb–Te and doped Sb-based compositions. The material properties of both are greatly influenced by their composition, and in a similar way. For both materials systems hold that the antimony content especially influences the crystallization rate, amorphous phase stability and media noise of the phase-change material. Compositions rich in antimony generally show high crystallization rates, low archival life stability and high media noise. The material properties are further influenced by the presence of dopants like tellurium, germanium, gallium, indium or tin. Germanium and tellurium reduce the crystallization rate, but are essential to increase the amorphous phase stability. Dopants like tin or indium are added to increase the crystallization rate or to adjust the optical constants.