Acoustic wave device with IDT electrode including al metal layer and high acoustic impedance metal layer

An acoustic wave device comprising:

• an energy confinement layer;
• a piezoelectric layer on the energy confinement layer and made of Y-cut X-propagation lithium tantalate having a cut angle of equal to or more than about −10° and equal to or less than about 65°;
• and
• an IDT electrode on the piezoelectric layer;
• wherein
• the IDT electrode includes a plurality of electrode fingers, the plurality of electrode fingers including a multilayer body including an Al metal layer defined by an Al layer or an alloy layer including Al, and a high acoustic impedance metal layer that has a Young's modulus equal to or more than about 200 GPa and a higher acoustic impedance than an acoustic impedance of Al;
• the high acoustic impedance metal layer is located closer to the piezoelectric layer than the Al metal layer;
• the high acoustic impedance metal layer is an Mo layer, a W layer, or an Ru layer;
• the following Expression 2 is satisfied;
• and
• a combination of each coefficient of Expression 2 and a metal of the high acoustic impedance metal layer is a combination shown in Table 1 below:
• a0(2)(tLT−c0)2+a0(1)(tLT−c0)+b0≤aLT(2)(tLT−cLT)2+aLT(1)(tLT−cLT)+aM(2)(T−cM)2+aM(1)(T−cM)+dLT-M(tLT−cLT)(T−cM)+b Expression 2;
• TABLE 1
• METAL FORMING HIGH ACOUSTIC IMPEDANCE
• METAL LAYER
• COEFFICIENT
• Mo
• W
• Ru
• a0(2)
• 12315.2368
• a0(1)
• 2360.5990
• c0
• 0.2250
• b0
• 6287.8999
• aLT(2)
• −54656.6400
• −57176.4500
• −51809.7600
• aLT(1)
• 12799.3184
• 10774.6530
• 13577.4784
• cLT
• 0.2250
• 0.2250
• 0.2250
• aM(2)
• −256136.5936
• −252048.6950
• −177802.3113
• aM(1)
• −22623.1348
• −15612.4350
• −22797.2384
• cM
• 0.0844
• 0.0851
• 0.0816
• dLT-M
• 0.0000
• 72370.3153
• 0.0000
• b
• 6481.5295
• 6416.9953
• 6416.0623