Apparatus for reading fingerprint

A light beam emitted by a surface illuminant reaches the surface of a transparent base layer of a recess/projection detection optical element. A light beam emitted almost vertically is emitted to an air layer. A light beam incident on the transparent base layer at an angle larger than a total reflection angle returns to a two-dimensional photosensor at a portion contacting the air layer, but scatters in a transparent particle at a portion contacting the transparent particle. When a finger is brought into contact with a scattering reflection layer, the scattering reflection state does not change in an area corresponding to a valley of a fingertip. As indicated by an arrow, an amount of reflected light beam is large. In an area corresponding to a ridge of the fingertip, the light beam scattered by the transparent particle is absorbed. The amount of reflected light beam is small, as indicated by an arrow. An image having bright and dark portions optically emphasized in correspondence with the valley and ridge of the fingertip of the finger can be obtained.

BACKGROUND OF THE INVENTION
 The present invention relates to a reading apparatus for reading the shape
 or position of a recess or projection of a target object having a fine
 recess or projection such as a valley or ridge of a fingertip.
 A structure described in Jpn. Pat. Appln. KOKAI Publication No. 6-325158 is
 conventionally known as a reading apparatus for reading the shapes or
 positions of fine recesses or projections such as valleys or ridges of a
 fingertip. As shown in FIG. 16, this apparatus has a two-dimensional
 photosensor 2 disposed on a surface of a light source or an illuminant 1.
 An optical fiber bundle plate 3 having a bundle of a plurality of optical
 fibers 3a is formed on the two-dimensional photosensor 2. A
 light-reflecting plate 4 is disposed on the optical fiber bundle plate 3.
 The two-dimensional photosensor 2 has a light-shielding plate 2c having an
 openings 2b on a transparent substrate 2a. Sensor portions 2d are formed
 on the light-shielding plate 2c. The light-reflecting plate 4 is made of a
 transparent material sheet and has a plurality of V-grooves 4b on each of
 which a light-reflecting-layer 4a made of an aluminum or the like is
 deposited. A portion between the two adjacent V-grooves 4b is constituted
 by a projection 4d having a flat upper surface 4c and a substantially
 trapezoidal section.
 Almost all the components of this reading apparatus are flat to obtain a
 low-profile structure. As indicated by arrows in FIG. 16, parallel light
 beams are emitted vertically from the upper surface of the surface
 illuminant 1 and transmitted to the upper surfaces 4c of the
 light-reflecting plate 4 through the openings 2b of the two-dimensional
 photosensor 2 and optical fibers 3a of the optical fiber bundle plate 3.
 The transmitted light beams are reflected by the light-reflecting layers
 4a on the V-grooves 4b of the light-reflecting plate 4. These reflected
 light beams come into the adjacent optical fibers 3a other than the
 light-transmitting portion (optical fiber 3a) of the optical fiber bundle
 plate 3 and are incident on the sensor portions 2d of the two-dimensional
 photosensor 2. In this case, the beams are reflected by the upper surfaces
 4c of the projections 4d of the light-reflecting plate 4 which correspond
 to the recesses (valleys) of the fingertip, and the beams are absorbed at
 the upper surfaces 4c which contact to the projections (ridges) of the
 fingertip. Therefore, an image having bright and dark portions optically
 emphasized in correspondence with the recesses and projections of the
 fingertip, thereby reading the fingerprint.
 In the conventional reading apparatus of this type, the parallel beams are
 emitted vertically from the upper surface of the surface illuminant 1 and
 transmitted to the upper surface of the light-reflecting plate 4 through
 the openings 2b of the two-dimensional photosensor 2 and the optical
 fibers 3a of the optical fiber bundle plate 3. The light beams reflected
 by the upper surfaces 4c of the projections 4d of the light-reflecting
 plate 4 are reflected by the light-reflecting layer 4a of the V-grooves 4b
 of the light-reflecting plate 4 and come into the adjacent optical fibers
 3a other than the optical fiber 3a having undergone transmission. The
 incident angle at the optical fiber 3a having a small light reception
 angle increases to result in a large loss. This makes it difficult to
 obtain a sufficiently high contrast. In addition, to make the light beams
 reflected by the upper surfaces 4c of the projections 4d of the
 light-reflecting plate 4 come into the optical fibers 3a of the optical
 fiber bundle plate 3 which are located at the predetermined positions and
 strike the sensor portions 2d of the two-dimensional photosensor 2 which
 are located at the predetermined positions in a prescribed manner, the
 projections 4d of the light-reflecting plate 4, the optical fibers 3a of
 the optical fiber bundle plate 3, and the sensor portions 2d of the
 two-dimensional photosensor 2 must be accurately positioned in a
 one-to-one correspondence, resulting in a low productivity and a high
 cost.
 BRIEF SUMMARY OF THE INVENTION
 It is an object of the present invention to provide an apparatus capable of
 reducing an optical loss in reading a fingerprint or the like, eliminating
 positioning among the respective components, and improving the
 productivity.
 According to the present invention, there is provided a reading apparatus
 comprising:
 a light source;
 a photosensor having a transparent base layer formed on the light source,
 the photosensor having a plurality of photosensor portions formed on the
 base layer and a resin layer covering the photosensor portions; and
 a scattering reflection layer formed on the photosensor,
 wherein light emitted by the light source and scattered and reflected by
 the scattering reflection layer is incident on each photosensor portion.
 Additional objects and advantages of the invention will be set forth in the
 description which follows, and in part will be obvious from the
 description, or may be learned by practice of the invention. The objects
 and advantages of the invention may be realized and obtained by means of
 the instrumentalities and combinations particularly pointed out
 hereinafter.

DETAILED DESCRIPTION OF THE INVENTION
 First Embodiment
 FIG. 1 is an enlarged sectional view showing part of a reading apparatus
 according to the first embodiment of the present invention. This reading
 apparatus can read the shapes and/or positions of recesses or projections
 of a target object having fine recesses and/or projections. In the
 following embodiment, the reading apparatus will exemplify a fingerprint
 reading apparatus for reading a fingerprint. This fingerprint reading
 apparatus has a two-dimensional photosensor 12 on a light source or
 surface illuminant 11. A recess/projection detection optical element 13 is
 mounted on the two-dimensional photosensor 12. The surface illuminant 11
 comprises an edge light type backlight used in an electroluminescence
 panel or a liquid crystal display device. Although not shown, the edge
 light type backlight typically has a light-reflecting plate on the bottom
 surface of a light guide plate, one point light source such as a
 light-emitting diode is disposed at a position adjacent to an edge of the
 light guide plate, and an opposite side to the light guide plate of the
 point light source is covered with a light-reflecting sheet.
 The recess/projection detection optical element 13 has a scattering
 reflection layer 14. In the optical element 13, a large number of
 transparent spherical particles 16 made of a transparent resin (e.g.,
 acrylic resin) or glass and located in tight contact with each other or
 spaced apart from each other at a small gap are adhered to the upper
 surface of a transparent base layer 15 made of a transparent resin (e.g.,
 acrylic resin) or glass through a transparent adhesive layer 17.
 The transparent spherical particles 16 adhered to the transparent base
 layer 15 constitute the scattering reflection layer 14. The function of
 the scattering reflection layer 14 will be described later. The adhesive
 layer 17 which fixes the transparent particles 16 may be an adhesive sheet
 or double-coated tape. An alternative adhesive layer may be a layer coated
 with a thermo-setting or ultraviolet-curable adhesive. When the latter
 adhesive layer is used, the adhesive layer 17 is hardened upon setting the
 thermo-setting adhesive or curing the ultraviolet-curable adhesive. Even
 if the transparent particles 16 are pressed by a finger, the adhesive
 layer 17 will not deform.
 The recess/projection detection optical element 13 can be manufactured as
 follows. The adhesive layer 17 is formed on the upper surface of the
 transparent base layer 15 by printing, transfer, roll coating, or the
 like. The transparent particles 16 are sprinkled while the adhesive layer
 17 is not hardened. When the thermo-setting adhesive is used, the adhesive
 layer 17 is heated. When the ultraviolet-curable resin is used, the
 adhesive layer 17 is hardened upon irradiation of ultraviolet rays. The
 recess/projection detection optical element 13 can be very efficiently
 manufactured. In this case, since the transparent particles 16 can be
 sprinkled appropriately sparsely, optical interference between the
 transparent particles 16 can be prevented.
 The two-dimensional photosensor 12 has a structure in which a plurality of
 sensor portions (in FIG. 1, only two sensor portions are shown by 20A,
 20B) are arranged in a matrix. The two-dimensional photosensor 12 has a
 transparent substrate (transparent base layer) 21 made of a transparent
 resin (e.g., acrylic resin) or glass. A bottom gate electrode 22 serving
 as a light-shielding electrode made of chromium or aluminum is formed for
 each sensor portion 20A or 20B on the upper surface of the transparent
 substrate 21. A bottom gate insulating film 23 made of silicon nitride is
 formed on the entire upper surface of the substrate 21 which includes the
 electrodes 22. A semiconductor layer 24 made of amorphous silicon is
 formed on an upper surface portion of the bottom gate insulating film 23
 which corresponds to the center of the bottom gate electrode 22. n.sup.+
 -type silicon layers 25 are respectively formed on the two sides of the
 upper surface of the semiconductor layer 24. Source and drain electrodes
 26 and 27 as light-shielding electrodes made of chromium or aluminum are
 formed on the upper surfaces of the n.sup.+ -type silicon layers 25 and
 the upper surface of the bottom gate insulating film 23 which is close to
 the upper surfaces of the n.sup.+ -type silicon layers 25. A top gate
 insulating film 28 made of silicon nitride is formed on the entire surface
 of the resultant structure. A top gate electrode 29 as a transparent
 electrode made of ITO or the like is formed on the upper surface portion
 of the top gate insulating film 28 which almost corresponds to each
 semiconductor layer 24. An overcoat film 30 made of silicon nitride is
 formed on the entire surface of the resultant structure. In this
 two-dimensional photosensor 12, when a light beam is incident at random
 from the lower surface side, this light beam passes through a
 light-transmitting portion excluding.both the bottom gate electrode 22
 made of the light-shielding electrode and the source and drain electrodes
 26 and 27. The light beam is shielded by the bottom gate electrode 22 and
 is not directly incident on the semiconductor layer 24.
 In this fingerprint reading apparatus, the light beam emitted from the
 upper surface of the surface illuminant 11 passes through the
 light-transmitting portion of the two-dimensional photosensor 12. The
 transmitted light beam is incident on the lower surface of the
 recess/projection detection optical element 13. This incident light beam
 is scattered and reflected by the surface (i.e., the boundary between the
 surface and air) of the scattering reflection layer 14 of the
 recess/projection detection optical element 13. As shown in FIG. 2, when a
 finger (not shown in FIG. 1) is in tight contact with the scattering
 reflection layer 14, the finger is irradiated from below at random, and
 the scattered light beam and the reflected light beam from an area
 corresponding to the valley of the fingertip are transmitted through the
 top gate electrode 29 made of the transparent electrode near the valley of
 the fingertip and are incident on the incident surface of the
 semiconductor layer 24 below the top gate electrode 29 between the source
 and drain electrodes 26 and 27.
 The function of the scattering reflection layer 14 will be described below
 with reference to FIG. 2. A light beam emitted by the surface illuminant
 11 reaches the surface of the transparent base layer 15 of the
 recess/projection detection optical element 13. The light beam emitted
 almost vertically from the surface illuminant 11 is emitted to the air
 layer between the particles 16 directly or through the transparent
 particles 16. The light beam incident on the transparent base layer 15 at
 an angle larger than the total reflection angle is totally reflected at a
 portion contacting the air layer and returned to the two-dimensional
 photosensor 12 side. The light beam at a portion contacting the
 transparent particle 16 enters into the transparent particle 16, repeats
 total reflection in the transparent particle 16, and scatters. For this
 reason, when the finger is not in contact with the scattering reflection
 layer 14, each transparent particle 16 of the scattering reflection layer
 14 is opaque and whitish. When a finger 31 is brought into contact with
 the scattering reflection layer 14, no change in scattering reflection
 state occurs in an area corresponding to a valley 31a of the fingertip. As
 indicated by an arrow C in FIG. 2, an amount of reflected light is large.
 A light beam is transmitted from the transparent particles 16 to a ridge
 31b of the fingertip and is absorbed.by the ridge 31b, thereby greatly
 reducing the amount of reflected light, as indicated by an arrow D in FIG.
 2.
 When an amount of light incident on the semiconductor layer 24 of the
 sensor portion 20A or 20B of the two-dimensional photosensor 12 is equal
 to or larger than a preset amount of light (threshold value), the optical
 detection state of the sensor portion 20A or 20B is set as a bright state;
 otherwise, the optical detection state of the sensor portion 20A or 20B is
 set as a dark state. An image having the bright and dark portions
 optically emphasized in correspondence with the valley and ridge of the
 fingertip of the finger 31, thereby reading the fingerprint of the finger
 31.
 As described above, in this fingerprint reading apparatus, the
 recess/projection detection optical element 13 having the scattering
 reflection layer 14 made of the large number of transparent particles 16
 is formed on the two-dimensional photosensor 12. Even if the light beams
 from the upper surface of the surface illuminant 11 are emitted at random,
 the image having the bright and dark portions optically emphasized in
 correspondence with the valley(s) and ridge(s) of the fingertip of the
 finger 31 can be obtained. In this case, no optical fiber bundle plate is
 used, unlike the conventional case. The optical loss in reading the
 fingerprint can be reduced, and the positioning precision between the
 components can be less strict.
 The reduction in optical loss in reading the fingerprint will be described
 below. Of all light beams emitted at random from the upper surface of the
 surface illuminant 11, only the light beam shielded by the bottom gate
 electrode 22 does not contribute fingerprint reading, and the remaining
 light beams can contribute to fingerprint reading. The loss in these
 remaining light beams can rarely occur. Since the light beams are emitted
 at random from the upper surface of the surface illuminant 11, light
 utilization efficiency can be increased. More specifically, since the
 transparent substrate 21 of the two-dimensional photosensor 12 has a
 certain thickness, the light beams emitted at random from the upper
 surface of the surface illuminant 11 below the bottom gate electrode 22
 can also be used as beams for reading the fingerprint. To the contrary, in
 the conventional case, the parallel beams emitted vertically from the
 upper surface of the surface illuminant 1 below the light-shielding plate
 2c and transmitted to the upper surface of the light-reflecting plate 4
 cannot be used as beams for reading the fingerprint.
 The reason why the positioning precision of the components can be less
 strict will be described below. The width of the valley 31a of the
 fingertip of the finger 31 is about 100 .mu.m, and the width of the ridge
 31b is about 200 .mu.m. Assume that the width (channel direction) of the
 sensing part of the sensor portion 20A or 20B (part of the semiconductor
 layer 24 between the electrodes 26, 27) of the two-dimensional photosensor
 12 is set to fall within the range of about 10 to 30 .mu.m, and that the
 pitch is set to fall within the range of about 30 to 100 .mu.m and
 preferably about 50 to 80 .mu.m. In this case, one to three sensor
 portions 20A and 20B, and preferably at least one, i.e., about two sensor
 portions can be arranged for the valley 31a having a smaller width (about
 100 .mu.m) of the valley and ridge 31b of the fingertip of the finger 31.
 When the diameter of the transparent particle 16 of the recess/projection
 detection optical element 13 is set to fall within the range of 1 to 30
 .mu.m, e.g., about 5 .mu.m, a plurality of transparent particles 16 can be
 arranged at the position corresponding to each sensor portion 20A or 20B.
 With this arrangement, positioning between the two-dimensional photosensor
 12 and the recess/projection detection optical element 13 can be almost
 eliminated.
 The operation of the two-dimensional photosensor 12 will be described
 below. In each sensor portion 20A or 20B, the bottom gate electrode (BG)
 22, the semiconductor layer 24, the source electrode (S) 26, the drain
 electrode (D) 27, and the like constitute a bottom gate type transistor.
 The top gate electrode (TG) 29, the semiconductor layer 24, the source
 electrode (S) 26, the drain electrode (D) 27, and the like constitute a
 top gate type transistor. That is, the sensor portions 20A and 20B are
 constituted by photoelectric transducer transistors in which the bottom
 gate electrode (BG) 22 and the top gate electrode (TG) 29 are formed on
 the lower and upper side of the semiconductor layers 24, respectively. The
 equivalent circuit of the sensor portions 20A and 20B is shown in FIG. 3.
 Referring to FIG. 3, when a positive voltage (e.g., +10V) is applied to the
 bottom gate electrode (BG) while a positive voltage (e.g., +5V) is kept
 applied between the source electrode (S) and the drain electrode (D), a
 channel is formed in the semiconductor layer 24 to flow a drain current
 I.sub.DS. In this state, when a negative voltage (e.g., -20V) having a
 level enough to make the channel formed by the electric field of the
 bottom gate electrode (BG) disappear is applied to the top gate electrode
 (TG), the electric field from the top gate electrode (TG) acts in a
 direction to eliminate the channel formed by the electric field of the
 bottom gate electrode (GB), thereby pinching-off the channel. At this
 time, when the semiconductor layer 24 is irradiated with a light beam from
 the top gate electrode (TG) side, the electron-hole pairs are induced in
 the semiconductor layer 24 on the top gate electrode (TG) side. The
 electron-hole pairs are accumulated in the channel region of the
 semiconductor layer 24 to cancel the electric field of the top gate
 electrode (TG). A channel is then formed in the semiconductor layer 24 to
 flow the drain current I.sub.DS. This drain current I.sub.DS changes in
 accordance with a change in incident light amount of the semiconductor
 layer 24.
 As described above, in this two-dimensional photosensor 12, the electric
 field from the top gate electrode (TG) acts in a direction to prevent
 channel formation using the electric field of the bottom gate electrode
 (BG) to pinch-off the channel. The drain current I.sub.DS obtained when no
 light beam is incident can be greatly reduced, e.g., to about 10.sup.-14
 A. The difference between the drain current I.sub.DS obtained when no
 light beam is incident and the drain current I.sub.DS obtained when a
 light beam is incident can be made sufficiently large. As described above,
 the amount of light incident on the semiconductor layer 24 is equal to or
 larger than the preset amount of light (threshold value), a large drain
 current I.sub.DS flows to set the optical detection state of the sensor
 portion 20A or 20B to the bright state; otherwise, a small drain current
 I.sub.DS flows to set the optical detection state of the sensor portion
 20A or 20B to the dark state. Therefore, the image having bright and dark
 portions optically emphasized in correspondence with the valley or ridge
 of the fingertip of the finger 31, thereby reading the fingerprint of the
 finger 31.
 In the two-dimensional photosensor 12, each sensor portion 20A or 20B can
 have both a sensor function and a selection transistor function. These
 functions will be briefly described below. When a voltage of, e.g., ov is
 applied to the top gate electrode (TG) while a positive voltage (+10V) is
 kept applied to the bottom gate electrode (BG), holes are discharged from
 the trap level between the semiconductor layer 24 and the top gate
 insulating film 28 to allow refresh or reset operation. More specifically,
 when the reading apparatus is continuously used, the trap level between
 the semiconductor layer 24 and the top gate insulating film 28 is buried
 with the holes generated upon irradiation and the holes injected from the
 drain electrode (D). A channel resistance set while no light beam is
 incident is reduced, and the drain current I.sub.DS obtained when no light
 beam is incident increases. Therefore, the top gate electrode (TG) is set
 at 0V to discharge these holes to allow reset operation.
 When the positive voltage is not applied to the bottom gate electrode (BG),
 no channel is formed in the bottom transistor. Even if a light beam is
 incident, no drain current I.sub.DS flows to set the nonselected state.
 More specifically, by controlling the voltage applied to the bottom gate
 electrode (BG), the selected state and the nonselected state can be
 controlled. In the nonselected state, when 0V is applied to the top gate
 electrode (TG), the holes can be discharged from the trap level between
 the semiconductor layer 24 and the top gate insulating film 28 to allow
 reset operation in the same manner as described above.
 As a result, as shown in FIGS. 4A to 4D, for example, the top gate voltage
 VTG is controlled to fall within the range of 0V to -2V to allow control
 of the sensed state and the reset state. The bottom gate voltage V.sub.BG
 is controlled to fall within the range of 0V to +10V to allow control of
 the selected state and the nonselected state. That is, by controlling the
 top gate voltage V.sub.TG and the bottom gate voltage V.sub.BG, each
 sensor portion 20A or 20B of the two-dimensional photosensor 12 can have
 both the function serving as a photosensor and the function serving as the
 selection transistor.
 In the above embodiment, the recess/projection detection optical element 13
 is arranged separately from the two-dimensional photosensor 12. The
 present invention is not limited to this. For example, as shown in FIG. 5,
 the plurality of transparent particles 16 may be adhered to and arranged
 on the flat upper surface of the overcoat film 30 of the two-dimensional
 photosensor 12 through the adhesive layer 17. That is, the
 recess/projection detection optical element constituted by the transparent
 particles 16 and the adhesive layer 17 may be formed integrally on the
 flat upper surface of the overcoat film 30 of the two-dimensional
 photosensor 12. When the bottom gate insulating film 23, the top gate
 insulating film 28, and the overcoat film 30 of the two-dimensional
 photosensor 12 are formed by CVD, the upper surface of the overcoat film
 30 becomes uneven, although not shown. In this case, a transparent resin
 such as acrylic resin is applied to the upper surface of the overcoat film
 30 to form a transparent layer having the flat upper surface, and the
 plurality of transparent particles 16 may be formed on the upper surface
 of this transparent layer through the adhesive layer 17. Alternatively,
 for example, acrylic resin may be applied to the upper surface of the
 surface illuminant 11 to form the transparent substrate 21 of the
 two-dimensional photosensor 12, thereby integrally forming the
 two-dimensional photosensor 12 on the surface illuminant 11.
 In the embodiment shown in FIG. 1, the scattering reflection layer 14 is
 constituted by the large number of transparent particles 16. The
 scattering reflection layer 14 is not limited to this. Various
 arrangements may be employed. For example, a recess/projection detection
 optical element 44 as shown in FIG. 6 is constituted by a large number of
 parallel optical fibers 43 each having a core 41 and a cladding 42
 covering the core 41. These optical fibers 43 may be independently and
 directly mounted and arranged on the two-dimensional photosensor 12 or may
 be brought into tight contact and integrated with a resin or the like and
 may be arranged and mounted on the two-dimensional photosensor 12.
 Alternatively, a recess/projection detection optical element 55 shown in
 FIG. 7 is constituted by a transparent sheet 53 containing spherical
 cavities 54 filled with a gas such as air. To manufacture this
 recess/projection detection optical element 55, transparent sheets 51 and
 52 having hemispherical cavities are formed and so bonded as to match the
 hemispherical cavities. In this case, scattering and reflection occur on
 the surface of each cavity. The shape of the cavity 54 is not limited to
 the spherical shape, but can be a triangular prismatic, polyhedral, or
 columnar shape. To form a scattering reflection layer, a material sealed
 in the cavity is not limited to the gas, but can be a liquid or solid
 material if the material has a refractive index lower than that of the
 transparent sheet 53.
 Second Embodiment
 FIG. 8 is an enlarged sectional view showing a part of a fingerprint
 reading apparatus according to the second embodiment of the present
 invention. The same reference numerals as in the embodiment shown in FIG.
 1 denote the same parts in the second embodiment, and a detailed
 description thereof will be omitted.
 The second embodiment has substantially the same structure as that of the
 first embodiment except that a transparent conductive layer 32 made of ITO
 or the like is formed on a two-dimensional photosensor 12, and a
 recess/projection detection optical element 113 is formed on the
 transparent conductive layer 32. The recess/projection detection optical
 element 113 is made of a thin sheet having a thickness of about 200 .mu.m
 or less. The transparent conductive layer 32 serves as an electro-static
 proof layer and is grounded to an appropriate lead wire (not shown). The
 transparent conductive layer 32 is integrally formed on the upper surface
 of an overcoat film 30 of the two-dimensional photosensor 12 or the lower
 surface of a transparent base layer 115 of the recess/projection detection
 optical element 113 by deposition or the like. A large number of elongate
 projections or ridges 116 having a substantially hemispherical section are
 formed parallel on the upper surface of the transparent base layer 115
 made of acrylic resin or glass. The large number of projections 116
 constitute a scattering reflection layer 114 to be described later.
 In this fingerprint reading apparatus, the transparent conductive layer 32
 is formed on the two-dimensional photosensor 12 and grounded. Even if the
 apparatus has a low-profile structure in which the recess/projection
 detection optical element 113 having a thickness of about 200 .mu.m or
 less is in tight contact with the two-dimensional photosensor 12, strong
 static electricity can be discharged from a finger (not shown) brought
 into tight contact with the recess/projection detection optical element
 113 through the transparent conductive layer 32. Therefore, the operation
 error of and damage to the sensor portions of the two-dimensional
 photosensor 12 due to this strong static electricity can be prevented.
 The operation of the fingerprint reading apparatus shown in FIG. 8 will be
 described with reference to FIG. 9. Light beams emitted at random from the
 upper surface of a surface illuminant 11 are transmitted through the
 transparent conductive layer 32 and the light-transmitting portion of the
 recess/projection detection optical element 113. These light beams are
 incident on the lower surface of the recess/projection detection optical
 element 113. A finger 31 placed in tight contact with the projections 116
 of the recess/projection detection optical element 113 is irradiated with
 these incident light beams. The light beams reflected by the surfaces of
 the projections 116 are transmitted through the transparent conductive
 layer 32 and top gate electrodes 29 made of transparent electrodes located
 near the transparent conductive layer 32. The transmitted light beams are
 incident on semiconductor layers 24 located below the top gate electrodes
 29. In this case, the light beams incident on the lower surface of the
 recess/projection detection optical element 113 are reflected by the
 surfaces of the projections 116 once to several times (mainly multiple
 reflection). In principle, total reflection occurs at a portion
 corresponding to a valley 31a of the fingertip of the finger 31 placed in
 tight contact with the projections 116, and scattering and transmission
 occur at a portion corresponding to a ridge 31b of the fingertip of the
 finger 31.
 More specifically, since the light beams are emitted at random from the
 upper surface of the surface illuminant 11, light beams are reflected by
 the surfaces of the projection portions 116 corresponding to the valley
 31a of the fingertip of the finger 31 and are incident on the neighboring
 semiconductor layer 24, as indicated by arrows W.sub.1, W.sub.2, and
 W.sub.3 in FIG. 9. Some light beam is reflected once on the surface of the
 projection 116 corresponding to the valley 31a of the fingertip of the
 finger 31 and incidents on the neighboring semiconductor layer 24, as
 indicated by an arrow W.sub.4. This light beam is the minority. In any
 case, a large number of light beams are incident on the semiconductor
 layer 24 located near the valley 31a of the fingertip of the finger 31. On
 the other hand, as indicated by arrows B.sub.1, B.sub.2, and B.sub.3 in
 FIG. 9, light beams which are to be reflected several times on the
 surfaces of the projections 116 corresponding to the ridge 31b of the
 fingertip of the finger 31 are reflected and finally scattered and
 transmitted. A light beam which is about to be reflected once by the
 surface of the projection 116 corresponding to the ridge 31b of the
 fingertip of the finger 31 is directly transmitted without reflection, as
 indicated by an arrow B.sub.4. The light beams are rarely incident on the
 semiconductor layer 24 close to the ridge 31b of the fingertip of the
 finger 31. When the amount of light incident on the semiconductor layer 24
 is equal to or larger than the preset amount of light (threshold value),
 the optical detection state of the sensor portion is set as the bright
 state; otherwise, the optical detection state of the sensor portion is set
 as the dark state. An image having the bright and dark portions optically
 emphasized in correspondence with the valley and ridge of the fingertip of
 the finger 31 is obtained, thereby reading the fingerprint of the finger
 31.
 The recess/projection detection optical element shown in FIG. 8 can be
 formed integrally on the two-dimensional photosensor 12, and FIG. 10 shows
 its modification. After the top gate electrode 29 and the overcoat film 30
 of the two-dimensional photosensor 12 are formed, the transparent
 conductive film 32 is formed on the overcoat film 30 by sputtering or the
 like. The resultant structure is accommodated in a mold to integrally mold
 the recess/projection detection optical element 113 on the surface of the
 transparent conductive film 32. If the upper surfaces of the projections
 116 of the recess/projection detection optical element 113 must be flat,
 one or both of the top gate insulating film 28 and the overcoat film 30
 may be formed by spin coating.
 To form the recess/projection detection optical element 113 separately from
 the two-dimensional photosensor 12, a bottom gate insulating film 23, a
 top gate insulating film 28, and the overcoat film 30 of the
 two-dimensional photosensor 12 are normally formed by sputtering or CVD.
 When they are formed by such dry deposition, the upper surfaces of the
 films 23, 28, and 30 are made uneven, as shown in FIG. 10. That is, each
 sensor portion is made thicker than a portion between the sensor portions,
 and the surface of the overcoat film 30 is made uneven. In this case, the
 transparent conductive film 32 may be directly formed on the uneven
 surface of the overcoat film 30 by deposition or the like. Alternatively,
 although not shown, a transparent planarizing layer (not shown) may be
 formed on the uneven upper surface of the overcoat film 30, and the
 transparent conductive film 32 may be formed on this planarizing layer. To
 form the transparent planarizing layer on the upper surface of the
 overcoat film 30, a sheet-like transparent conductive layer 32 may be
 adhered to the upper surface of the planarizing layer through a
 transparent adhesive. Alternatively, a sheet-like transparent conductive
 layer 32 may be adhered to the lower surface of the transparent base layer
 115 of the recess/projection detection optical element 113 through a
 transparent adhesive.
 In the above embodiment, the transparent conductive layer 32 is formed on
 the upper surface of the two-dimensional photosensor 12 or the lower
 surface of the recess/projection detection optical element 113. The
 present invention is not limited to this. For example, as shown in FIG.
 11, a transparent conductive layer 132 may be formed on the upper surfaces
 of the projections 116 of the recess/projection detection optical element
 113 along these upper surfaces by deposition or the like. Alternatively,
 transparent conductive layers may be formed on any two or all of the upper
 surface of the two-dimensional photosensor 12 and the lower and upper
 surfaces of the recess/projection detection optical element 113.
 In the above embodiment, the sectional shape of the projection 116 of the
 recess/projection detection optical element 113 is substantially
 hemispherical. The present invention is not limited to this. For example,
 as shown in FIGS. 12A to 12D, the sectional shape of an arc as part of a
 circle, the sectional shape of part of a parabola, the sectional shape of
 part of an ellipse, and the sectional shape of a rectangular equilateral
 triangle may be used. As shown in FIGS. 13A to 13C, the truncated shapes
 obtained by truncating the top portions of the projections 116 shown in
 FIGS. 12A to 12C to obtain flat surfaces 116a parallel to the lower
 surface of the transparent base layer 115 may be used. Although not shown,
 the top portions of the projections 116 shown in FIG. 8 may be constituted
 by flat surfaces parallel to the lower surface of the transparent base
 layer 115. As shown in FIG. 13D, the top portions of the projections 116
 shown in FIG. 12D may be replaced with surfaces 116b having a sectional
 shape of an arc as part of a circle, as shown in FIG. 13D.
 In the above embodiment, the recess/projection detection optical element
 113 has a structure in which the large number of elongate projections 116
 are arranged parallel on the upper surface of the transparent base layer
 115. The present invention is not limited to this. For example, as shown
 in FIG. 14, a large number of hemispherical projections (protrusions) 116
 may be staggered on the upper surface of the transparent base layer 115,
 thereby constituting the recess/projection detection optical element 113.
 Although not shown, the shape is not limited to the hemispherical shape,
 but can be the shape of a doom constituting part of a sphere, part of a
 stereoscopic shape obtained by rotating a parabola about a predetermined
 axis, part of a stereoscopic shape obtained by rotating an ellipse about a
 predetermined axis, or the shape of a quadrangular prism. These shapes may
 be truncated, as shown in FIGS. 13A to 13D.
 In the above embodiment, the upper surface of the recess/projection
 detection optical element 113 is made uneven. The present invention is not
 limited to this. For example, as shown in FIG. 15, the recess/projection
 detection optical element 113 may be constituted by a structure in which a
 high-reflection layer 62 having a plurality of laminated layers having
 different refractive indices is formed on the upper surface of a
 transparent plate 61 made of acrylic resin or glass. For example, the
 high-reflection film 62 has a structure in which an aluminum oxide layer
 62a, a zinc oxide layer 62b, and a magnesium fluoride layer 62c are formed
 by deposition, coating, or the like on the upper surface of the
 transparent plate 61 in the order named. The thickness of each of the
 layers 62a, 62b, and 62c falls within the range of about several ten to
 several hundred .ANG.. The high-reflection layer 62 increases reflection
 using interference of reflected light beams at the boundary surfaces of
 the layers 62a, 62b, and 62c. High reflection occurs at the upper surface
 portion of the high-reflection layer 62 which is in tight contact with the
 valley of the fingertip of the finger, and low reflection occurs at a
 portion corresponding to the ridge of the fingertip of the finger. An
 image having the bright and dark portions optically emphasized in
 correspondence with the valley or ridge of the fingertip of the finger can
 be obtained, thereby reading the fingerprint of the finger. Note that a
 low-reflection layer may be formed on the lower surface of the transparent
 plate 61.
 As has been described above, according to the present invention, a
 recess/projection detection optical element having a scattering reflection
 layer on at least the upper surface is formed on a photosensor, and the
 conventional optical fiber bundle plate is not used. Therefore, the
 optical loss in reading the fingerprint or the like can be reduced, and
 positioning precision of the components can be less strict.
 Additional advantages and modifications will readily occur to those skilled
 in the art. Therefore, the invention in its broader aspects is not limited
 to the specific details and representative embodiments shown and described
 herein. Accordingly, various modifications may be made without departing
 from the spirit or scope of the general inventive concept as defined by
 the appended claims and their equivalents.