US 6,713,941 B2Granted

Surface acoustic wave element

AssigneeSeiko Epson Corporation

InventorsKatsuhiro Itakura, Akihiro Hachigo, Hideaki Nakahata, Satoshi Fujii, Shinichi Shikata

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Abstract

A surface acoustic wave (SAW) device that is suitable for mass production and that has excellent operational performance at the superhigh-frequency range. The SAW device comprises (a) a diamond layer 3; (b) a ZnO layer 4, with a thickness of tz, formed on the diamond layer 3; (c) interdigital transducers (IDTs) 5, which excite and receive a SAW, formed on the ZnO layer 4; and (d) an SiO2 layer 6, with a thickness of ts, formed on the ZnO layer 4 so that the SiO2 layer can cover the IDTs 5. The structure of the SAW device is determined by specific numeric ranges of the parameters kh1 and kh2, which are given in equations kh1=3·2π·(tz/λ) and kh2=3·2π·(ts/λ), where λ signifies the wavelength of the fundamental wave of the second Sezawa mode of the SAW. The SAW device uses the third harmonic of the second Sezawa mode of the SAW excited.

A surface acoustic wave (SAW) device, being specified by the conditions of:

(a) the SAW device comprising:
(a1) a diamond layer;
(a2) a ZnO layer:
(a2a) being formed on the diamond layer;
and
(a2b) having a thickness of tz,
(a3) interdigital transducers (IDTs):
(a3a) being formed on the ZnO layer;
and
(a3b) having the function of exciting and receiving a SAW, and
(a4) an SiO2 layer:
(a4a) being formed on the ZnO layer so that the SiO2 layer can cover the IDTs;
and
(a4b) having a thickness of ts
(b) providing a two-dimensional orthogonal-coordinate system, in which the axis of abscissa represents kh1 and the axis of ordinate represents kh2, where kh1 is expressed by the equation kh1=3·2π(tz/λ) and kh2 is expressed by the equation kh2=3·2π(ts/λ), λsignifying the wavelength of the fundamental wave of the second Sezawa mode of the SAW;
(c) in the orthogonal-coordinate system connecting sequentially;
point A given by the coordinates “kh1=0.30 and kh2=0.87”;
point B given by the coordinates “kh1=0.54 and kh2=0.87”;
point C given by the coordinates “kh1=0.60 and kh2=0.87”;
point D given by the coordinates “kh1=0.81 and kh2=0.97”;
point E given by the coordinates “kh1=1.16 and kh2=1.20”;
point F given by the coordinates “kh1=1.52 and kh2=0.93”;
point G given by the coordinates “kh1=1.69 and kh2=0.77”;
point H given by the coordinates “kh1=1.31 and kh2=0.59”;
point I given by the coordinates “kh1=1.04 and kh2=0.50”;
point J given by the coordinates “kh1=0.68 and kh2=0.40”;
point K given by the coordinates “kh1=0.63 and kh2=0.33”;
point L given by the coordinates “kh1=0.30 and kh2=0.63”;
and
point A
to provide the range ABCDEFGHIJKLA surrounded by 12 lengths of lines;
(d) structuring the SAW device so that kh1 and kh2 can fall in the range ABCDEFGHIJKLA including the surrounding 12 lengths of lines;
(e) using the third harmonic of the second Sezawa mode of the SAW excited
(f) the third harmonic of the second Sezawa mode of the SAW having propagation velocity, denoted by v, of 8,000 to 12,000 m/s;
(g) the IDTs having a plurality of comb-tooth-shaped digit electrodes of which:
(g1) the sum of the width of a digit electrode and the distance between the neighboring digit electrodes is expressed as
dm+df=(3·v)/(2·f0),
where dm:
the width of the digit electrode,
df:
the distance between the neighboring digit electrodes, and
f0:
the center frequency of the third harmonic of the second Sezawa mode of the SAW:
(g2) the sum “dm+df” is 1.0 μm or more;
and
(g3) the ratio “dm/(dm+df)”, which is referred to as the metal ratio, satisfies the formula 0.15<dm/(dm+df)<0.3 or the formula 0.7<dm/(dm+df)<0.85;
and
(h) the center frequency of the third harmonic of the second Sezawa mode of the SAW being 5 to 12 GHz.

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Abstract

Claims2