This application claims the benefit of European Patent Application No. 19161626.7, filed on Mar. 8, 2019, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present document relates to a sensor (e.g., a pressure sensor and/or an acoustic sensor, e.g., for a microphone) having a membrane electrode, a counter-electrode, and at least one spring interposed between the membrane electrode and the counter-electrode.

The document also relates to a method for manufacturing a sensor such as the sensor above.

BACKGROUND

A pressure sensor, such as an acoustic sensor, may comprise at least two electrodes (e.g., at least one membrane electrode and at least one counter-electrode). For example, a membrane electrode may be deformable, as a consequence, of the pressure (e.g., caused by sound). A counter-electrode may be non-deformable and fixed to a fixed structure. The membrane electrode may be connected to a fixed structure of the sensor in correspondence of the membrane rim.

The membrane electrode may be fabricated so as to present a tensile stress, e.g., to counterbalance the attractive electrostatic forces between the membrane electrode and the counter-electrode.

By virtue of the deformation caused by the pressure, high concentrations of stress may be defined in correspondence of the membrane rim. Accordingly, robustness of the sensors is in general reduced.

Due to the assembly processes, thermal expansion of different package materials and aging of the materials package cause additional stress between the membrane electrode and the counter-electrode. This additional stress changes the compliance of the membrane, reducing, for example, the sensitivity. This leads to significant yield loss.

Since the rim of the membrane electrode is fixed to the structure, large areas of the membrane are limited in their movement. Hence, the overall signal amplitude is reduced. Therefore, the chip delivers limited signal and/or the signal to noise ratio (SNR) is reduced. In general, the sensor needs to be designed larger than necessary, hence increasing costs to reach satisfactory signal and SNR value.

Moreover, tolerances during manufacturing cause the membrane electrode to have non-perfect positioning. Therefore, it is often necessary to perform a calibration to adapt the particular position of the membrane with respect to the structure. Therefore, it is difficult to achieve the result of different sensors, which are nominally identical, to operate exactly at the same sensitivity, without calibration. Calibration, however, implies complications both in software and in hardware.

Further, the stress on the membrane also depends on the external temperature. Therefore, it is difficult to achieve a sensor which is always performing under all climatic conditions.

The limited mechanical robustness can lead to field failures and requires additional measures, limitations and costs. Thicker membranes need therefore to be used.

It is therefore intended to find out techniques which reduce at least in part impairments as those discussed above.

SUMMARY

In accordance with an example, a sensor is provided comprising a structure, a membrane electrode, which is deformable as a consequence of pressure and which is in contact with the structure, a counter-electrode mechanically connected to the structure and separated from the membrane electrode by a gap, and at least one spring that is between the membrane electrode and the counter-electrode so as to exert an elastic force between the membrane electrode and the counter-electrode.

In accordance with an aspect, the sensor may comprise a flexible membrane connection mechanically connecting the membrane electrode to the structure.

In accordance with an example there is provided a method for manufacturing a semiconductor pressure-sensor and/or acoustic sensor, comprising:

preparing a first element on a substrate, wherein the first element is chosen between a membrane electrode and a counter-electrode;

preparing at least one spring element to abut on the first element;

preparing a second element, so that the at least one spring element abuts on the second element and is elastically connected to the first element and the second element, wherein the second element is a counter-electrode or a membrane electrode, wherein the second element is chosen between the counter-electrode and the membrane electrode which is not chosen for the first element.

