Electrically Trimmable Phase Change Ge2Sb2Te5 Resistors With Tunable Temperature Coefficient of Resistance

Electrically trimmable resistors have been manufactured using the phase change alloy Ge2Sb2Te5. High resistivity values (about 1 m Omega cm) and almost zero temperature coefficient of resistance (TCR) have been obtained using resistors with hcp phase of metallic behavior and converting a small region of the film into the fcc phase, with opposite trend of resistance versus temperature. The conversion into the fcc phase has been obtained through two electric pulses, the first for melting and quenching in the amorphous phase and the second for crystallization in the fcc semiconductive phase. Theoretical considerations together with the experimental measurements allow to determine the proper ratio between the metallic and the semiconductive phase required to obtain a target resistance and temperature dependence. For example, a resistor almost independent on the temperature can be achieved by electrical trimming, increasing the resistance of about 10% of the initial value. The resistor layout has been optimized through electro-thermal simulations, to achieve the modification of the resistors structure only in a confined region. Experimental results confirm the theoretical expectations and demonstrate that phase change materials can be effectively used to obtain reversible electrically trimmable resistors with adjustable TCR.