For phase change random access memory (PCRAM) cells, it is important to know the contact resistance of phase change materials (PCMs) to metal electrodes at the contacts. In this letter, we report the systematic determination of the specific contact resistance (ρ c ) of doped Sb 2 Te and Ge 2 Sb 2 Te 5 to TiW metal electrodes. These data are reported for both the amorphous and the crystalline states of these PCMs. The temperature and voltage dependences of ρ c are also studied. A detailed understanding of these contacts is essential for the scaling, design, device modeling, and optimization of PCRAM cells. Index Terms-Cross bridge Kelvin resistor (CBKR), doped Sb 2 Te, Ge 2 Sb 2 Te 5 , phase change materials (PCMs), specific contact resistance (ρ c ).

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Electrical characterisation of metal to Phase Change Material (PCM) contacts is necessary for optimum power transfer during switching of a Phase Change Random Access Memory (PCRAM) cell. In this article, titanium tungsten (Ti o . 3Wo . 7 ) to two phase change materials; doped-Sb-Te and GezSb z Te, are characterised using Circular Transfer Length Method (CTLM) structures. A metal lift off process with a maximum process temperature of 120°C allows processing of these CTLM structures below the crystallization temperature of PCM used. The specific contact resistance for TiW-PCM contacts with PCM in amorphous (high resistive) and crystalline (low resistive) phases is extracted from these CTLM measurements.

In this article we report on the change in contact resistance of TiW to doped-Sb2Te in the 5nm-50nm thickness range of the PCM layer. This interface is characterized both in the amorphous and in crystalline state of doped-Sb 2 Te. The nature of the interface is characterized by electrical contact resistance measurements and is expressed in terms of specific contact resistance, ρ C . Results from the measurements on these structures with illumination indicated the existence of a space-charge region at the metal amorphous doped-Sb 2 Te interface. I.

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