This invention relates to an imaging device for an authentication apparatus using the finger veins, the palm veins, the veins of the back of the hand or the fingerprint, and an imaging device for the portable terminal such as the mobile phone, the PDA or the PC or the image reader such as the facsimile or the scanner.
A finger authentication apparatus is described below as a typical case.
The password has been widely used in an authentication method for identifying an individual person. Now that a more accurate authentication technique is in demand, however, the biological authentication is closely watched. This authentication method, which uses the features of a part of a living creature or the motion thereof (biological information), is high in security and utility and free of oblivion or loss as compared with the key or the password. The research is underway for the authentication method using the biological information including the fingerprint, the iris, the facial contour, the palm contour, the veins of the back of the hand, the palm veins, the finger veins, the voiceprint, the signature (handwriting) or the smell. Especially, the method using the finger veins has drawn special attention in recent years.
The authentication apparatus using the finger veins, as described in JP-A-2003-30632, employs the image of the finger veins picked up using the near infrared ray. According to JP-A-2003-30632, a finger is held between a near infrared light source and an imaging unit, and the light that has passed through the finger is converted to an image by the imaging unit. The blood vessel pattern image thus obtained is collated with the blood vessel pattern image registered in advance thereby to authenticate an individual person. In another apparatus configuration according to the method disclosed in JP-A-2005-323892 and JP-A-2006-288872, a light source and an imaging unit are arranged on the same side of a finger, and a blood vessel pattern image is obtained from the light scattered in the finger. In this configuration, an open space is available in the upper part of the imaging unit thereby to alleviate the sense of oppression on the part of the user while at the same time reducing both the size and thickness of the authentication apparatus.
This finger vein authentication is currently used for the bank ATM or the entry/exit management device, and another promising application is portable terminals such as a mobile phone. To realize this application, however, the imaging device including the light source is required to be reduced in thickness on the one hand and equipped with the display function at the same time.
As a method for realizing this application, a structure is available in which a detection element array is arranged on a light source. JP-A-2005-242841 and JP-A-2005-276030 disclose an imaging device integrated with a light source in which a detection element array is arranged on the display and held between an object to be imaged and the display. The use of the detection element array transmitting the display light makes it possible to produce an image by radiating the display light on the object at the time of picking up an image. JP-A-2006-86333, on the other hand, discloses an imaging device integrated with a light source having a structure in which a detection element array is similarly arranged on a display and held between an object and the display and in which the elements of the detection element array and the display elements are arranged in staggered fashion so that light can be passed between the elements of the detection element array.
Still another structure of an imaging device integrated with a light source having a light-emitting unit layer arranged on a detection element substrate is described in JP-A-5-14620. In this structure, a space where light can be transmitted is formed between the light-emitting units of the light-emitting unit layer in opposed relation to the detection elements. The light emitted from the light-emitting units is reflected from an object and detected by the detection elements through the space between the light-emitting units. The light-emitting units each have a structure in which a light-emitting element is held between a transparent electrode and a metal electrode with the transparent electrode arranged on the object side and the metal electrode on the detection element side. This metal electrode is covered by the bottom surface and the side surface of the detection element, thereby realizing a structure in which the direct light from the light-emitting units fails to reach the detection elements.
In the structure described in JP-A-2005-242841 and JP-A-2005-276030, however, the detection element array is required to transmit the light, and therefore, cannot be increased in detection sensitivity, thereby posing the problem that the light reflected from the object cannot be fully detected. Also, the fact that the display and imaging light are attenuated poses the problem that the display image quality is deteriorated and the power is consumed for radiation of the light not used. Also, the radiated light is transmitted through the detection element array, and therefore, a pseudo signal is likely to be generated by partial detection of the radiated light. Further, the display and the imaging operation cannot be performed at the same time.
The structure described in JP-A-2006-86333, on the other hand, encounters the problem that the fill factor of the detection element array cannot be increased and the light reflected from the object cannot be sufficiently detected. Also, since the display and imaging light is output through the detection elements, the problems are posed that the image displayed is dark, the display position resolution is deteriorated or otherwise the image quality is adversely affected, and the power is consumed for radiation of the unrequired light. Further, the realization of a structure transmitting the light only through the detection elements increases the cost of the detection element array and requires a high fabrication technique while at the same time reducing the yield.
The structure of JP-A-5-14620 poses the problem that the need of a metal electrode larger than the light-emitting element increases the size of the light-emitting unit, and therefore, the light-emitting units cannot be arranged densely. Also, in the case where organic EL elements each having a thickness of several 10 nm to several 100 nm are used as light-emitting elements, the electrodes undesirably come into contact with each other at the ends or corners thereof and the normal function of the light-emitting units may not be exhibited, resulting in a lower yield. To overcome this problem, a high production control technique and a high fabrication technique are required, thereby leading to a high apparatus cost. Another problem of the organic EL elements is that a multilayer structure having a current and hole transport layer and a buffer layer may be required between the light-emitting layer and the electrode, and cannot be realized by the structure described in JP-A-5-14620, or if realized, an unsatisfactory end layer structure would deteriorate the characteristics including the dark current.