Acoustic wave element, branching filter and communication module

An acoustic wave element comprising:

• a piezoelectric substrate,
• an IDT comprising a first comb-shaped electrode and a second comb-shaped electrode which are located on an upper surface of the piezoelectric substrate, and
• two or more capacitance elements which are located on the upper surface of the piezoelectric substrate and are electrically connected to the IDT, wherein
• the first comb-shaped electrode comprises
• a first bus bar and
• a plurality of first electrode fingers extending from the first bus bar,
• the second comb-shaped electrode comprises
• a second bus bar and
• a plurality of second electrode fingers extending from the second bus bar,
• In the first comb-shaped electrode and the second comb-shaped electrode, the plurality of first electrode fingers and the plurality of second electrode fingers mesh with each other,
• the first electrode fingers have tips facing the second comb-shaped electrode across first gaps in their extending direction,
• the second electrode fingers have tips facing the first comb-shaped electrode across second gaps in their extending direction,
• the capacitance elements comprises
• two or more first counter electrodes which are connected to the first comb-shaped electrode and
• two or more second counter electrodes which are connected to the second comb-shaped electrode and face the first counter electrodes across third gaps,
• the direction from the first counter electrodes through the third gaps toward the second counter electrodes is a reverse direction from the direction from the first comb-shaped electrode through the first gaps toward the second comb-shaped electrode and from the direction from the first comb-shaped electrode through the second gaps toward the second comb-shaped electrode, and
• the capacitance elements satisfy the following formula (D) where
• the total number of the first gaps and the second gaps is n (n≧2), lengths and widths of the i-th first gap and second gap among the first gaps and the second gaps which are counted in order from one end of the IDT are d, and w, (1n),
• the total number of the third gaps is m (m≧2), and
• the length and width of the j-th third gap are Dj and Wj (1≦j≦m):
• 0
• <
• ∑
• j
• =
• 1
• m
• 
• 
• W
• j
• D
• j
• 2
• <
• 2
• 
• ∑
• i
• =
• 1
• n
• 
• 
• w
• i
• d
• i
• 2
• (
• D
• )

An acoustic wave element comprising:

• a piezoelectric substrate,
• an IDT provided comprising a first comb-shaped electrode and a second comb-shaped electrode which are located on an upper surface of the piezoelectric substrate, and
• a pair of reflectors which are located on the upper surface of the piezoelectric substrate so as to sandwich the IDT therebetween, wherein
• the first comb-shaped electrode comprises
• a first bus bar and
• a plurality of first electrode fingers extending from the first bus bar,
• the second comb-shaped electrode comprises
• a second bus bar and
• a plurality of second electrode fingers extending from the second bus bar,
• in the first comb-shaped electrode and the second comb-shaped electrode, the plurality of first electrode fingers and the plurality of second electrode fingers mesh with each other,
• the first electrode fingers have tips facing the second comb-shaped electrode across first gaps in their extending direction,
• the second electrode fingers have tips facing the first comb-shaped electrode across second gaps in their extending direction,
• the reflectors comprise
• first counter electrodes which are connected to the first comb-shaped electrode and
• second counter electrodes which are connected to the second comb-shaped electrode and face the first counter electrodes,
• one electrodes of the first counter electrodes and the second counter electrodes comprise a plurality of third electrode fingers which extend toward the other electrodes of the first counter electrodes and the second counter electrodes and have tips facing the other electrodes across the third gaps in their extending direction, and
• the direction from the first counter electrodes across the third gaps toward the second counter electrodes is a reverse direction from the direction from the first comb-shaped electrode through the first gaps toward the second comb-shaped electrode and from the direction from the first comb-shaped electrode through the second gaps toward the second comb-shaped electrode.