A crystal unit includes a package, a crystal element, and a temperature sensor. The crystal element includes a crystal blank and a pair of excitation electrodes on a pair of major surfaces of the crystal blank and is air-tightly sealed in the package. The temperature sensor is mounted in the package. The crystal blank includes a crystal plane inclined relative to the major surfaces in at least a portion of the side surfaces.

An oscillator includes a first resonator element, a first circuit element configured to oscillate the first resonator element to generate a first oscillation signal, a first package which is configured to house the first resonator element and the first circuit element, and has a mounting surface and a mounting terminal disposed on the mounting surface, a second resonator element an oscillation frequency of which is controlled based on the first oscillation signal, and a second package which houses the second resonator element and is provided with the second package mounted on the mounting surface of the first package.

An oscillator includes a resonation element, a temperature sensitive element, a first package that houses the resonation element and the temperature sensitive element and is airtightly sealed, and a second package that houses the first package and is airtightly sealed. The first package includes a first base having a first recessed portion that is provided on one main surface side and a first lid that is joined to the first base so as to close an opening of the first recessed portion. The second package includes a second base having a second recessed portion that is provided on one main surface side and a second lid that is joined to the second base so as to close an opening of the second recessed portion.

A piezoelectric oscillator includes a base member on which a piezoelectric resonator is mounted, a first lid member that seals the piezoelectric resonator on the base member, and a second lid member that seals the first lid member on the base member. The first lid member and the second lid member are each joined to the base member.

An oscillator includes a first package that is airtightly sealed, a second package that is housed in the first package and airtightly sealed, a resonation element that is housed in the second package, and a circuit element that is housed in the first package in a state of being positioned outside the second package and electrically connected to the resonation element and has an oscillation circuit and a temperature compensation circuit. In addition, the first package includes a base having two main surfaces and a recessed portion provided on one of the main surfaces, and a lid joined to the base so as to close the opening of the recessed portion. The circuit element is attached to the base, and the second package is attached to the circuit element.

A resonator element includes an SC-cut quartz crystal substrate having a thickness t, and an excitation electrode disposed on a principal surface of the quartz crystal substrate, the principal surface being square or rectangular in shape, a side of which has a length L, 28L/t60 is satisfied.

A crystal oscillator includes a crystal resonator; an inverting amplifier configured to be coupled between a pair of excitation electrodes of the crystal resonator; and a control circuit configured to initiate an alarm and raise gain of the inverting amplifier in a case where an index value for representing oscillation amplitude of the crystal resonator in an oscillation state is equal to or lower than a reference value.

A crystal unit includes an AT-cut crystal element that has a planar shape in a rectangular shape and a part as a thick portion. The crystal element includes a first end portion, a depressed portion, the thick portion, and a second end portion in this order from a side of one short side in viewing a cross section taken along a longitudinal direction near a center of the short side. The depressed portion is a depressed portion disposed from the thick portion toward the first end portion side, depressed with a predetermined angle a and subsequently bulged, and connected to the first end portion.

A crystal unit includes an AT-cut crystal element that has a planar shape in a rectangular shape and a part as a thick portion. The crystal element includes a first end portion, a first depressed portion, the thick portion, a second depressed portion, and a second end portion in this order from a side of one short side, in viewing a cross section taken along a longitudinal direction near a center of the short side. The first depressed portion is a depressed portion disposed from the thick portion toward the first end portion side, depressed with a predetermined angle a and subsequently bulged, and connected to the first end portion. The second depressed portion is a depressed portion disposed from the thick portion toward the second end portion side, depressed with a predetermined angle b and subsequently bulged, and connected to the second end portion.

An oscillator includes a resonation element, a temperature sensitive element, a first package that houses the resonation element and the temperature sensitive element and is airtightly sealed, and a second package that houses the first package and is airtightly sealed. The first package includes a first base having a first recessed portion that is provided on one main surface side and a first lid that is joined to the first base so as to close an opening of the first recessed portion. The second package includes a second base having a second recessed portion that is provided on one main surface side and a second lid that is joined to the second base so as to close an opening of the second recessed portion.