密着露光法を用いたサブミクロン電極の製作と1.1GHz発振の検討

抄録

Attempts to achieve higher UHF and microwave surface acoustic wave interdigital transducers (SAWIDT's) have led to fabrication techniques such as optical direct projection, electron beam and X-ray lithography. Where multiple copies of transducers are required, optical contact printing is simple and advantageous. This paper describes the successful fabrication of 0. 7 μm linewidth SAW IDT's by conventional photographic contact printing and the characteristics of the 0. 7 μm linewidth SAW filter and 1. 1 GHz SAW delay line oscillator. Experimental conditions ; photomasks (Table 1 and Fig. 1), IDT pattern, photo resist, mask alignment and photo process are described. Problems of submicron linewidth formation by contact printing are discussed from both the experimental and theoretical point of view. It was found that the most important factor is a good contact between photomask and substrate. Diffraction of ultraviolet light takes place when the contact is poor. Experimentally, a small gap cannot be avoided (the average gap width is about 2 μm in our experiment), but, by using the SAW transducer pattern in Fig. 1 (d) which decreases the influence of diffraction, in comparison with pattern No. C-1 in Fig. 1(c), we have successfully obtained 0. 7 μm linewidth SAW IDT's (Fig. 9). 0. 7 μm linewidth transducers were made using ST-quartz substrate. The transducers and the chip pattern are showed in Fig. 2. The electrode is 50 nm aluminum metallization. The frequency characteristic of this filter are given in Fig. 13. The 1. 1 GHz SAW delay line oscillator shown in Fig. 14(a) consists of a 0. 7 μm linewidth SAW filter and an amplifier. 1. 1 GHz spectrum of this oscillator is shown in Fig. 14 (b). The short term stability (gate time=1 sec) is 8×10^&lt-8&gt . In conclusion, it was found that conventional photolithographic contact printing is an important fabrication technique by which SAW devices can be economically produced which operate above 1 GHz.