Surface sensor
The invention relates to a sensor for detection of properties and structures of an organic tissue and its surface, e.g. a fingerprint sensor comprising a chosen number of sensor electrodes at chosen positions for coupling to a finger tissue and its surface having a size less or comparable to the size of the structures, characteristics or properties of the finger tissue or surface, and a processing unit including electronic circuitry connected to said electrodes for detection of the voltage at, or the current flow in the electrodes, thereby providing for detection and collection of information of related capacitance, impedance, electromagnetic field, fingerprint, tissue aliveness or other biometric, physical, physiological, thermal or optical or characteristics or properties of the tissue or its surface positioned over the electrodes, the processing unit being mounted on one side of a substrate and the electrodes being embedded in said substrate, the substrate including through going first, second and third conductive paths between said sensor electrodes and said measurement circuitry. The substrate is made from a polymer material such as Polyimide, implemented as a rigid or a flexible multi layer build-up substrate, said first, second, and third conductive paths are constituted by through going substrate sections of a chosen size and material.
1. A sensor unit for measuring a surface of an object, the sensor unit comprising:
a first dielectric layer;
a signal processing unit;
a second dielectric layer located between said first dielectric layer and said signal processing unit, the second dielectric layer having a first side that faces the first dielectric layer and a second side opposite the first side;
a set of first electrodes having predetermined sizes and positions at the first side of the second dielectric layer;
a set of second electrodes having predetermined sizes and positions at the first side of the second dielectric layer; and
a plurality of conductive sections separated by dielectric material in said second dielectric layer, each of the plurality of conductive sections extending from the first side to the second side and having:
a first end galvanically coupled to one of said first electrodes or to one of said second electrodes and
a second end having one of a plurality of predetermined positions on the second side of said second dielectric layer; and
electrically conductive components connected to said conductive sections at said predetermined positions of said second ends of the conductive sections, the electrically conductive components providing galvanic connection to the signal processing unit,
wherein each of said electrically conductive components of a set of electrically conductive components that provide electrical connection for the second electrodes is offset, in a direction parallel to the first side or the second side of the second dielectric layer, from a center of a corresponding one of said second electrodes; and
wherein said signal processing unit is adapted to detect a voltage or current at said first electrodes and second electrodes.
2. The sensor unit according to claim 1 , wherein the dielectric material is polyimide.
3. The sensor unit according to claim 1 , further comprising an additional layer comprising at least two sub-layers, wherein at least one of the two sub-layers comprises a pattern of additional conductive sections adapting the positions of the second ends of the plurality of conductive sections to positions of connection points of the signal processing unit.
4. The sensor unit according to claim 1 , wherein at least one of said second electrodes has dimensions that are larger than dimensions of at least one of the first electrodes.
5. The sensor unit according to claim 4 , wherein each of the second electrodes is provided with a connection point at the second side of the second dielectric layer for coupling to the processing unit.
6. The sensor unit according to claim 4 , wherein the thickness of the first layer over at least one second electrode is reduced.
7. The sensor unit according to claim 1 , wherein the first dielectric layer comprises openings over at least one of said electrodes providing galvanic contact between the electrode and the object.
8. The sensor unit according to claim 1 , wherein said electrically conductive components are connected to conductors on a flexible printed circuit board (PCB) or printed circuit, the conductors providing a connection between the electrically conductive components and a corresponding interface on the signal processing unit, wherein the corresponding interface on the signal processing unit is offset from the electrically conductive components.
9. The sensor unit according to claim 8 , wherein the signal processing unit is positioned on the same side of the flexible PCB or printed circuit relative to the electrically conductive components.
10. The sensor unit according to claim 8 , wherein the signal processing unit is positioned on the opposite side of the flexible PCB or printed circuit relative to the electrically conductive components.
11. The sensor unit according to claim 8 , wherein the flexible PCB or printed circuit comprises a number of components and a coupling interface to external equipment.
12. The sensor unit according to claim 1 , wherein at least one of the first dielectric layer and the second dielectric layer is flexible.
13. A method for producing a sensor unit, comprising the steps of:
depositing liquid polyimide on a plane glass surface and hardening the polyimide material to form a first layer;
depositing a second layer on said first layer by:
applying a pattern of electrically conductive material constituting first electrodes on the first layer and
depositing additional liquid polyimide to provide insulation between the first electrodes and hardening the additional polyimide material;
depositing a third layer by:
applying a pattern of electrically conductive material constituting a number of conductors having one end electrically connected to said pattern of electrically conductive material in said second layer,
depositing further additional liquid polyimide material to provide insulation between the number of conductors and
hardening the further additional polyimide material; and
removing the first layer, second layer, and third layer from said glass surface, so as to provide a contact surface at a surface of said first layer.
14. The method according to claim 13 , including a step of applying an electrically conductive material to opposite ends of the number of conductors to form electrically conductive components for interfacing with a signal processing unit.