A silicon optical bench incorporating a tantalum-nitride thin-film resistor

Abstract

A new silicon optical bench (SiOB)—incorporating tantalum-nitride thin-film resistors (TNTFRs) for signal damping as well as terminating transmitted signals—has been developed. The SiOB has a deep V-groove for locating a lens, gold/platinum/titanium thin-film electrodes and gold–tin solder films for mounting a laser diode and a photodiode. The tantalum-nitride thin film for the TNTFRs is deposited by RF-magnetron reactive sputtering. The film was analyzed by both Auger electron spectroscopy and x-ray diffraction, and its composition is identified as Ta2N. The measured V-grooves have an average width of 1000.8 µm with 3σ variation of 1.2 µm. This result indicates that silicon anisotropic etching using fan-shaped patterns can fabricate precise V-grooves without producing crystal deviation. Moreover, the TNTFRs for damping have an average resistance of 9.74 Ω, a breakdown-current density of 2.00 × 1010 A m−2 and a temperature coefficient of resistance of 106 ppm °C−1; the corresponding values of TNTFR for termination are 48.1 Ω, 2.58 × 1010 A m−2 and 108 ppm °C−1. And the average change in resistance for damping after conducting reliability tests is less than 1.97%. Consequently, the developed SiOB is suitable for use in transmitter modules because it has precise V-grooves and TNTFRs with a low-variability resistance.