Air-bridge metal interconnection technology is used for upper level power supply line interconnections in GaAs LSI's to reduce the signal propagation delay time. This technology reduces both parasitic capacitance between the signal line and the power supply line, and propagation delay in the signal line to about 10% and about 50%, respectively, compared to conventional 3-level interconnections without air-bridges. Under standard load conditions (FI=FO=2, length of load line=2 mm), the air-bridge technique leads to gate propagation delays which are about 60% of those in conventional interconnections. We fabricated 2.1-k gate Gate Arrays and 4-kb SRAM's using the air-bridge structure to interconnect power supply lines. For a Gate Array with 0.7 µm gate Buried P-layer Lightly Doped Drain (BPLDD) FET's, the typical gate propagation delay under standard load conditions was about 110 ps with a dissipation power of 1.4 mW/gate. SRAM's with 05 µm gate BPLDD's had typical access time (tacc) of 1.5 ns with a dissipation power of 700 mW/chip.

GaAs 10 Gb/s 64:1 Multiplexer/Demultiplexer chip sets have been successfully developed. The 64-bit 156 Mb/s parallel data output or input of these chip sets can be directly connected to CMOS LSIs. These chip sets consist of a 10Gb/s 4: 1 MUX IC, a 10 Gb/s 1: 4 DEMUX IC, four 2.5 Gb/s 16: 1 MUX LSIs and four 2.5 Gb/s 1: 16 DEMUX LSIs. This multi-chip construction is adopted for low power dissipation and high yield. The basic circuit employed in the 10 Gb/s4: 1 MUX/DEMUX ICs is an SCFL circuit using 0.4 µm-gate FETs with a power supply of -5.2 V, and that in 2.5 Gb/s 16: 1 MUX/DEMUX LSIs is a DCFL circuit using 0.6 µm-gate FETs with a power supply of -2.0 V. These chip sets have functions for synchronization among these ICs and to enable bit shift to make the system design easier. In the 10 Gb/s 4: 1 MUX IC, a timing adjuster is adopted. This timing adjuster can delay the timing of the most critical path by 50 ps. Even if the delay times are out of order due to fluctuations in process, temperature, power supply voltage and other factors, this timing can be revised and the 4: 1 MUX IC can operate at 10 Gb/s. Furthermore, a 48-pin quad flat package for 10 Gb/s 4: 1 MUX/DEMUX ICs has been newly developed. The measured insertion loss is 1.7 dB (at 10 GHz), and the isolation is less than -20 dB (at 10 GHz). These values are sufficient in practical usage. Measurements of these chip sets show desirable performance at the target 10 Gb/s. The power dissipations of the 64: 1 MUX/DEMUX chip sets are 10.3 W and 8.2 W, respectively. These chip sets is expected to contribute to high speed telecommunication systems.

In order to establish design and measurement technologies for an LSI that features high speed operation and low power dissipation, GaAs 2.5 Gbps 16 bit MUX/DEMUX LSIs have been successfully developed. DCFL is employed as a basic gate in order to reduce the power dissipation. For the purpose of achieving stable operation against the transistor parameter deviation, a timing design called clock tracking is employed. Moreover, to ensure accurate performance measurement, a new measurement system is introduced. The measurement system consists of an error rate detector (ERD), a pulse pattern generator (PPG) and a high speed tester (HST). The performances tested by the measurement system show the power consumptions of MUX and DEMUX LSIs are 1.35 W and 0.95 W. Input phase margin of DEMUX LSI is 290 degrees at 2.5 Gbps operation. The technologies obtained through development of these MUX/DEMUX LSIs are applicable to other high speed and low power LSIs.