Integrated circuits utilizing piezoelectric elements can be advantageously constructed by bonding elements together via direct bonds. Such integrated circuits include an electro-acoustic hybrid integrated circuit such as a voltage controlled oscillator wherein a semiconductor substrate having an active element is bonded through direct bonding to a surface acoustic wave resonator or a quartz oscillator as an electro-acoustic element. A quartz device can also be provided which includes a quartz plate, excitation electrodes on opposite surfaces, and a holding member made of a material having a thermal expansion coefficient substantially equal to that of the quartz plate. The holding member is connected to the quartz plate by direct bonding without using any adhesives. Because the thermal expansion coefficients of the quartz plate and the holding member are equal, no thermal stress occurs in the bonding area. As a result, virtually no stress is applied to the quartz plate and the frequency-temperature characteristic can be improved. A piezoelectric filter according to the invention includes an oscillatory piezoelectric plate made of quartz, lithium tantalate, lithium niobate or lithium borate and having an oscillatory portion; a glass plate to which the piezoelectric plate is directly bonded; and first and second oscillatory electrode members which are provided on opposite faces of the oscillatory portion, respectively, such that at least one of the oscillatory electrode members is divided into a plurality of counter electrodes.