Ground-shielded measuring technique for accurate on-wafer characterization of RF CMOS devices

This paper presents a new test fixture with associated de-embedding procedure for efficient and accurate on-wafer device measurements at microwave frequencies. The fixture is based on a substrate shield and (i) provides an accurate common ground for N-port measurements, (ii) effectively reduces substrate carried coupling, (iii) gives well-defined parasitics for simplified de-embedding, and (iv) fits arbitrarily large devices. Due to these characteristics, the accompanying de-embedding technique requires only few in-fixture standards that can be fabricated with very high accuracy; even in standard CMOS processes. The technique can advantageously be applied to a wide range of commonly used processes, but highest performance improvement is achieved with low-resistivity substrates. The performance of the technique is demonstrated to 12 GHz in a 0.25 μm CMOS technology and conclusions are drawn.