Characterisation of the threshold voltage variation: a test chip and the results

This paper presents an inexpensive test structure for characterisation within wafer variability of the threshold voltage. The expense of measuring many transistors is reduced by analog multiplexing which allows one to perform the measurements with only one analog pin. Results of measurements in digital CMOS technology are presented. The importance of proper identification of spatial component of the threshold voltage variations is pointed out. Without this the characterisation of local fluctuations is usually inaccurate.