Comparison of self-aligned and non-self-aligned GaAs E/D MESFETs

The device characteristics and circuit performance of self-aligned GaAs E/D-MESFETs have been compared. The fabrication process for both devices is discussed. Electrical measurements across a 2-in wafer showed that an average self-aligned 40-μm-wide, 1-μm-long enhancement device has transconductance of 275±17 mS/mm, an intrinsic K -value of 16.3±2.7 mS/V, a series resistance of 0.88±0.1 Ω-mm, and a threshold deviation of 28 mV. Corresponding data for the non-self-aligned devices were 191±19 mS/mm, 10.3±1.4 mS/V, 1.2±0.2 Ω-mm, and 45 mV, respectively. An ECL-compatible 1-kb static RAM and a 4-kb static RAM were fabricated using both self-aligned and non-self-aligned processes for comparison. Using the self-aligned process, the power consumption of the 1-kb SRAM was 230 mW, compared to 530 mW for the non-self-aligned SRAM, while access times remained the same. Typical access times for self-aligned 4-b SRAM devices ranged from a minimum of 2.8 ns to a maximum of 3.8 ns. This 1-ns range is considerably less than that of a typical non-self-aligned device with 2.5 ns of access time scatter