Typically, an electronic chip is made by a microelectronic fabrication process, i.e. by the deposition of successive layers on a substrate and by the etching of certain of these layers, for example, by photolithography.
Here, the electronic chips concerned comprise thermal transducers capable of converting the temperature variation into a difference in potentials.
For example, electronic chips of this kind are used to make fingerprint detectors.
The present filing party knows of methods for calibrating these chips in which a normal transducer of the chip to be calibrated is placed in contact with a first element having a first thermal characteristic and a corresponding temperature variation ΔT1 is measured with the normal transducer.
The term “thermal characteristics” of an object or an element designates a characteristic that is a function of the thermal capacity and/or the thermal conductivity of this object or element.
These prior art elements also comprise the placing of the same normal transducer of the chip to be calibrated in contact with a second element having a second thermal characteristic and the measurement of a corresponding temperature variation ΔT2 with the same normal transducer and the read circuit of the chip to be calibrated.
For example, in the case of a fingerprint detector, the temperature variations ΔT1 and ΔT2 preferably correspond to the extreme variations that may be encountered in the normal use of the electronic chip. Thus, the variations ΔT1 and ΔT2 correspond respectively to the case in which the normal transducer is in contact with air and to the case in which it is directly in contact with water. Water is an element which best simulates the thermal conductivity that may be possessed by the epidermis of a finger. Indeed, the very great majority of the cells of the epidermis are constituted by water.
Besides, the values measured for the variations ΔT1 and ΔT2 vary from one chip to another, even if these electronic chips are identical. Here, the term “identical chips” designates chips that have been obtained by the same fabrication method. It is therefore necessary to renew the measurements of the variations ΔT1 and ΔT2 on each chip. This is a lengthy and painstaking task.
In addition, the values of the variations ΔT1 and ΔT2 are specific to each chip, and these values are recorded in the chip itself. This necessitates the use of a non-volatile memory in the chip making this chip more complex and costly to obtain.