In recent years, electrostatic induction-type vibration power generation devices which use a charged body called an electret have been actively developed.  This device includes an electret and electrodes provided so as to face a charged surface of the electret.  This device forms an electrostatic capacitance when an external electric field emitted from the charged surface of the electret induces electric charges on the counter electrodes.  When a relative position between the electret and the electrodes is changed by an external force in this device, the electrostatic capacitance changes and an electric current is created in a load connected thereto.  Thus, electric power can be obtained (for example, see Patent Literatures 1 to 3). 
When this vibration power generation device is used as a driving source of a small sensor, for example, it is possible to shorten a sensing interval and to reduce the size of the module by improving the power generation amount.  As a means of improving the power generation amount of the vibration power generation device, a method of obtaining a larger surface charge density than conventional corona discharge methods disclosed in Patent Literatures 1 to 3 is proposed (for example, see Patent Literature 4).  In this method, a spontaneous polarization of monocrystalline zinc oxide is used as an electret by focusing on the fact that the power generation amount is proportional to the square of a surface charge density of a charged body.  Based on the same reasons, as a means of obtaining a high surface charge density, a method of using a ferroelectric substance having high crystalline orientation as an electret is proposed (for example, see Patent Literature 5).  Further, a method of manufacturing an electret formed of a ferroelectric material, for applications to electret capacitor microphones is proposed (for example, see Patent Literature 6).