Mid-air haptic device with energy harvesting function and method for manufacturing said haptic device

Abstract

One aspect of the invention relates to a remote haptic device comprising a first transducer called an emitter configured to generate, under the effect of a control signal, ultrasonic waves reproducing the illusion of touch on human skin, a portion of the ultrasonic waves propagating in a first direction from the emitter towards a target area located at a distance from the haptic device and another portion of the ultrasonic waves propagating in a second direction opposite to the first direction. The haptic device is characterized in that it further comprises: A second transducer called a receiver, configured to receive and convert into an electrical current the ultrasonic waves propagating in the second direction, the emitter being disposed between the target area and the receiver.An energy harvesting unit electrically connected to the receiver and configured to receive the electrical current produced by the receiver. Figure to be published with the abbreviation: Figure 2,

Description

Title of the invention: Mid-air haptic device with energy harvesting function and method for manufacturing said haptic device TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a haptic device, and in particular to a haptic device comprising an energy harvesting function.

[0002] The invention finds applications in fields where vibrations cause tactile sensations such as in the field of video games, augmented reality, assistance or even the biomedical field. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] It is known, in the haptic field, to seek to produce or reproduce, by means of a device, called a haptic device, the sensations of touch felt, or perceived, by a user.

[0004] Among the existing haptic devices, we know those which provide tactile sensations in the air, therefore at a distance from the haptic device. These devices, also called "mid-air" devices in English, generally use a network of ultrasonic transducers which generate, under the effect of a control signal, an acoustic field focused in a target area of ​​the air and whose pressure is sufficient to produce vibrations felt by the user.

[0005] These MID-AIR haptic devices make it possible, for example, to simulate the feeling of a texture of a virtual object displayed on a screen when the user points to this virtual object with his finger, without touching the screen.

[0006] A common problem with mid-air haptic devices formed from an array of ultrasonic transducers is that each transducer generates not only a wave in the desired direction (i.e., in the air), but also a wave in the direction opposite to the desired direction, because these transducers are composed of membranes vibrating at a predefined frequency above a cavity.

[0007] To solve this problem, document US2017216887A1 describes an example of a mid-air haptic device. In addition to the ultrasonic transducer array previously mentioned, the device described in this document comprises a backing layer arranged on the rear face of the ultrasonic transducer array. The backing layer here designates the face facing the side opposite the target air area, the target air area being positioned at the front of the haptic device. The backing layer makes it possible to absorb, and therefore block, the ultrasonic waves propagating on the rear side of the transducer array. This allows to integrate this haptic device into a system worn by a user, in particular in a virtual reality headset, since the ultrasonic waves propagating towards the user are no longer dangerous for this user (they are stopped before reaching the user).

[0008] Another problem with these mid-air haptic devices, and haptic devices in general, is their energy consumption. Indeed, this point is key in haptic devices because they are very often embedded in devices with limited energy quantity, for example operating on battery. Summary of the invention

[0009] The invention provides a solution for reducing the energy consumption of mid-air haptic devices, by making it possible to create an electric current from the ultrasonic waves propagating in the opposite direction to the target area (thus these ultrasonic waves are used wisely instead of being lost) and by making it possible to receive and store this electric current. This allows this current to be used as an energy source.

[0010] According to a first aspect, the invention relates to a remote-type haptic device comprising a first transducer called a transmitter configured to generate, under the effect of a control signal, ultrasonic waves reproducing the illusion of touch on human skin, a portion of the ultrasonic waves propagating in a first direction going from the transmitter to a target area located at a distance from the haptic device and another portion of the ultrasonic waves propagating in a second direction opposite to the first direction, said haptic device being characterized in that it further comprises: • A second transducer called a receiver, configured to receive and convert into an electric current the ultrasonic waves propagating in the second direction, the transmitter being arranged between the target area and the receiver, • An energy recovery unit electrically connected to the receiver and configured to receive the electric current produced by the receiver.

[0011] Thus, the use of a transducer configured to produce a current under the effect of ultrasonic waves (the receiver) and placed on the trajectory of the ultrasonic waves propagating opposite the target area, i.e. towards the rear of the transmitter, allows energy production from these ultrasonic waves. In other words, the ultrasonic waves propagating towards the rear are now made functional instead of being unused, and therefore lost. This characteristic provides an improvement over the approaches of the prior art, since energy (the electric current) is now produced and reusable, in particular by the haptic device.

[0012] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the haptic device according to the first aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations. • The receiver is a transducer of the same type as the transmitter, the type being for example a piezoelectric transducer or a magnetostriction transducer. • The receiver has a resonant frequency equal to a resonant frequency of the transmitter plus or minus 500 Hz, preferably equal to a resonant frequency of the transmitter plus or minus 50 Hz. • Said resonant frequency is greater than or equal to 20 kHz, preferably equal to 100 kHz. • The receiver is separated from the transmitter by a distance less than or equal to 1000 pm, preferably less than or equal to 800 pm, preferably less than or equal to 500 pm, said distance being measured in the second direction between a rear face of the transmitter and a front face of the receiver. • The energy harvesting unit is electrically connected to the transmitter and configured to inject the electric current produced by the receiver into the transmitter, said electric current being used to produce at least part of the control signal of the transmitter. • Alternatively, the energy harvesting unit is electrically connected to an output track of the haptic device, the output track being intended to be electrically coupled to a power supply unit external to the haptic device. • The haptic device further comprises a protective layer configured to attenuate ultrasonic waves propagating in the second direction, the receiver being disposed between the transmitter and the protective layer. • The transmitter is a network of elementary transducers and the receiver is also a network of elementary transducers, each elementary transducer of the receiver being arranged opposite at least one of the elementary transducers of the transmitter. When the transmitter is an array of elementary transducers and the receiver is also an array of elementary transducers, • The network of elementary transducers forming the receiver has the same number of elementary transducers as the network of elementary transducers forming the transmitter, said number of elementary transducers being greater than 100, for example equal to 139. • The network of elementary transducers forming the receiver has, in top view, a shape identical to a shape of the network of elementary transducers forming the transmitter, said shape having two lateral dimensions, each lateral dimension being greater than or equal to 2 cm, preferably greater than or equal to 1 cm. • Each elementary transducer is a micro-machined piezoelectric ultrasonic transducer also called PMUT, the array of elementary transducers then being an array of micro-machined piezoelectric ultrasonic transducers also called PMUT array.

[0013] A second aspect of the invention relates to a method of manufacturing a remote type haptic device according to the invention comprising the steps of: • Manufacture of the transmitter, • Manufacture of the receiver, • Assembly of the transmitter and receiver such that in use the ultrasonic waves received and converted by the receiver are the ultrasonic waves generated by the transmitter propagating in the second direction, • Supply of the energy recovery unit, • Making the electrical connection between the energy recovery unit and the receiver.

[0014] According to one embodiment, the step of manufacturing the transmitter comprises the sub-steps of: • Supply of a first substrate, • For each PMUT of the transmitter: • Deposition of a sacrificial material on a first face, called the rear face, of the first substrate, and formation, in the sacrificial material, of an initial cavity, • Deposition of a membrane by growth, for example, of polycrystalline silicon on a second face of the first substrate opposite the first face of the second substrate, said membrane being configured to provide mechanical rigidity to the PMUT concerned, a thickness of said membrane being dimensioned to adjust a resonance frequency of the PMUT concerned, • Formation of the PMUT concerned on the membrane, comprising the deposition of a first electrode on the membrane deposited on the second face of the first substrate, the deposition of a piezoelectric layer on the first electrode, the deposition of a second electrode on the piezoelectric layer and the etching of the second electrode, the piezoelectric layer and the first electrode until reaching said membrane, so as to form patterns configured to convey the control signal of the PMUT concerned, • Formation of the cavity of the PMUT concerned by extending the bottom of the initial cavity to the membrane deposited on the second face of the first substrate, And the receiver manufacturing step including the sub-steps of: • Supply of a second substrate, • For each PMUT of the receiver: • Deposition of a sacrificial material on a first face, called the rear face, of the second substrate, and formation, in the sacrificial material, of an initial cavity, • Deposition of a membrane of the same material as the membrane material of each PMUT of the emitter on a second face of the second substrate opposite the first face of the second substrate, • Formation of the PMUT concerned on the membrane deposited on the second face of the second substrate, comprising the deposition of a first electrode on the polymer membrane, the deposition of a piezoelectric layer on the first electrode, the deposition of a second electrode on the piezoelectric layer and the etching of the second electrode, of the piezoelectric layer and of the first electrode until reaching said membrane, so as to form patterns configured to convey the control signal of the PMUT concerned, • Formation of the cavity of the PMUT concerned by extending the bottom of the initial cavity to the membrane deposited on the second face of the first substrate. BRIEF DESCRIPTION OF THE FIGURES

[0015] Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures in which:

[0016] The figure represents, in schematic form, an example of a mid-air type haptic device according to one or more embodiments of the invention,

[0017] [Fig.2] represents, in schematic form, a first embodiment of the device represented in [Fig.l], making it possible to generate a complex haptic effect and to improve energy recovery,

[0018] [Fig.3] represents an example in cross-sectional view of a PMUT type ultrasonic cell of the device represented in [Fig.2],

[0019] [Fig.4] represents measurement results showing the variation of the acoustic pressure generated by one of the ultrasonic transducers forming part of the device represented in [Fig.2] as a function of the distance from the front face of this device,

[0020] [Fig. 5] shows, in schematic form, a second embodiment of the device shown in [Fig. 1], making it possible to protect a user against the effects of ultrasonic pressure generated at the rear of the device,

[0021] [Fig.6] represents an example in cross-sectional view of a PMUT type ultrasonic cell of the device represented in [Fig.5],

[0022] [Fig.7] represents, in the form of a flowchart, steps of a manufacturing method according to the invention, making it possible to manufacture the device shown in [Fig.2],

[0023] Figures 8A to 8J show, in sectional view, sub-steps of the first step of the manufacturing method shown in [Fig.7]. DETAILED DESCRIPTION

[0024] The present invention relates to the field of remote-type haptic devices, also called mid-air haptic devices, and their manufacture. More particularly, the present invention aims to improve the energy efficiency of a mid-air haptic device, which allows this device to consume less energy than an existing mid-air haptic device for an identical haptic effect.

[0025] A remote or mid-air haptic device designates a device generating a haptic effect, that is to say a sensation of touch, at a distance, therefore in the air, using ultrasonic waves which stimulate the skin.

[0026] [Fig. 1] represents, in schematic form and in perspective, an example of a mid-air haptic device, also referred to as “device 1” hereinafter, according to one or more embodiments in accordance with the invention. This [Fig. 1] also illustrates, in a very schematic manner, the operating principle of the device 1.

[0027] As shown in [Fig.l], and in a manner common to all the embodiments of the device 1 presented subsequently, the device 1 comprises a first ultrasonic transducer 10 called transmitter 10, a second ultrasonic transducer 20 called receiver 20, and an energy recovery unit 30.

[0028] To facilitate the description, an orthonormal reference frame OXYZ is assigned to the device 1.

[0029] In this OXYZ reference frame, the OXY plane coincides with an upper face (in [Fig.l]) of the emitter 10 of the device 1 and the OZ axis coincides with a longitudinal axis of the device 1.

[0030] Subsequently, the terms “width”, “length”, “diameter” or “lateral dimension” designate dimensions measured in a plane parallel to the OXY plane. The terms “thickness” or “height” designate dimensions measured along the OZ axis.

[0031] In [Fig.l], the axis OZ is oriented towards the top of the figure, in the direction of a target zone C of the air space AIR located above the device 1. In practice, this air space AIR is located at the front of the device 1.

[0032] The upper face of the emitter 10 is in fact subsequently called “front face 10a of the emitter 10” and constitutes a front face of the device 1. With reference to [Fig.l], the face of the emitter 10 which is opposite the front face 10a of the emitter 10 is called “rear face 10b” of the emitter 10.

[0033] Furthermore, it is considered that an element is located “at the rear” of the transmitter 10 when it is positioned, in [Fig. 1], under the transmitter 10. Conversely, an element is located “at the front” of the transmitter 10 (and therefore of the device 1) when it is positioned, in [Fig. 1], above the transmitter 10.

[0034] Finally, the first direction DI is the direction going from the transmitter 10 towards the target zone C, therefore upwards in [Fig.l], and the second direction D2 is the direction going from the transmitter 10 towards the direction opposite to the target zone C, i.e. downwards, in [Fig.l]. In other words, the first direction DI is a direction oriented “towards the front” of the device 1, while the second direction is a direction oriented “towards the rear” of the device 1.

[0035] As illustrated in [Fig.l], the transmitter 10 receives, in operation, an electrical power Pem, which is equal to the product of a supply voltage (not shown in the figures) and a control current ie. This power determines the energy consumed by the transmitter 10.

[0036] The transmitter 10 is further configured to generate, under the effect of the control signal ie, non-audible ultrasonic waves O1 and O2.

[0037] By “non-audible” is meant a frequency of the ultrasonic waves O1, O2 strictly greater than 20 kHz, preferably greater than 40 kHz and for example equal to 100 kHz. This frequency of the ultrasonic waves generated by the transmitter 10 corresponds to the carrier frequency or resonance frequency of the transmitter 10.

[0038] A part 01 of these ultrasonic waves 01, 02, propagates in the first direction D1, therefore towards the front of the device 1, and is focused on the target zone C previously described. The target zone C is then located at a distance from the front face 10a of the transmitter 10 of between 10 cm and 40 cm, for example equal to 30 cm.

[0039] The transmitter 10 is configured so that the ultrasonic waves 01 generate on the target area C an acoustic pressure sufficient to reproduce the sensation of touch in a user U, when the latter approaches his finger (as illustrated in the example of [Fig.l]) of the target area C. The acoustic pressure created by the ultrasonic waves 01 at the target point C is thus at least equal to 200 Pa. This threshold value of 200 Pa corresponds to the smallest perceptible acoustic pressure.

[0040] As shown in [Fig.l], another part 02 of the ultrasonic waves 01, 02 generated by the transmitter 10 propagates in a second direction D2 opposite to the first direction D1, therefore towards the rear of the transmitter 10. These ultrasonic waves 02 directed towards the rear (also called “rear ultrasonic waves 02” hereinafter) are not functional in that they do not produce the haptic effect on the target area C.

[0041] The inventors identified that it was judicious to use these rear ultrasonic waves 02, conventionally unused and therefore lost, to produce an electric current irec and, therefore, to provide (or recover), an electric power Prec (and therefore an electric energy) capable of being consumed by the device 1 itself or another separate device.

[0042] For this, the receiver 20 is an ultrasonic transducer configured to receive the rear ultrasonic waves 02 and convert them into irec current.

[0043] As shown in [Fig.l], the receiver 20 is in practice arranged at the rear of the transmitter 10 (the latter then being arranged between the target zone C and the transmitter 10), and facing the transmitter 10. The term “facing” designates the configuration according to which at least a part of the transmitter 10 and the receiver 20 face each other.

[0044] Thus, since the receiver 20 is placed on the path of the rear ultrasonic waves 02 and it is configured as an ultrasonic wave receiver (and not as a transmitter), the rear ultrasonic waves 02 are received and converted into an electric current, here the current irec.

[0045] Concretely, the emitter 10 can be stacked on the receiver 20 to form an emissive-receptive ultrasonic structure.

[0046] Preferably, the transmitter 10 and the receiver 20 are transducers of the same type, that is to say that the transduction mode implemented by the transmitter 10 is based on the same physical phenomenon as that implemented by the receiver 20.

[0047] By way of example (and in a non-limiting manner), the types of transduction concerned may be transduction modes such as piezoelectric or electromagnetic (the physical phenomenon is then a magnetostriction phenomenon).

[0048] Preferably, the height, or distance, hio_2o between the transmitter 10 and the receiver 20 is as small as possible so that the receiver 20 picks up the greater part of the rear ultrasonic waves 02 generated by the transmitter 10. For assembly reasons, it is acceptable that the acoustic pressure produced by the rear ultrasonic waves on the front face 20a of the receiver 20 is at least equal to or greater than one fifth of the acoustic pressure of these rear ultrasonic waves on the rear face of the transmitter 10. By thus specifying the height hiO_2o between the transmitter 10 and the receiver 20, it is possible to increase the current irec produced by the transmitter 20, since these rear ultrasonic waves are received while being attenuated as little as possible by the environment present between the transmitter 10 and the receiver 20. In particular, this allows at least 20% of the energy consumed by the transmitter 10 to be recovered by the receiver 20.

[0049] The resonant frequency of the receiver 20 is advantageously identical to the resonant frequency of the transmitter 10. This makes it possible to optimize the conversion rate of the ultrasonic waves 02 into current irec, since the frequency of the rear ultrasonic waves coincides with the resonant frequency of the receiver 20.

[0050] Finally, the energy recovery unit 30 is electrically connected to the receiver 20 using an electrical connection 31 and configured to receive, via this electrical connection 31, the current irecp generated by the receiver 20.

[0051] The electrical connection 31 is for example a metal track.

[0052] The energy recovery unit in practice comprises an output track 32 (for example a metal track) configured to redistribute the current irec received and / or the power Prec generated by the receiver 20. This allows the electrical energy generated by the receiver 20 to be reusable, since the current irec can be taken via the output track 32.

[0053] According to a variant, the output track 32 of the recovery unit can be coupled to the transmitter 10. This allows the power Prec generated by the receiver 20 to be used by the transmitter 10 as a source of additional electrical power. Thus, the amount of energy that must be supplied to the device 1 to produce the haptic effect is reduced. The energy efficiency of this device 1 is therefore improved.

[0054] According to another variant, not shown in the figures, the output track 31 of the recovery unit is coupled to an energy source external to the device 1 (in other words to an energy source not forming part of the device 1) to supply energy to another device. Thus, the device 1 is a producer of electrical energy.

[0055] This latter variant is for example advantageous when the device 1 is intended to be embedded in a portable device, for example to be integrated into a virtual reality headset worn on the user's head. Indeed, the current i produced by the device can serve as a control signal or as a source of energy for other elements of the virtual reality headset. This makes it possible to limit the amount of energy that must be supplied to the virtual reality headset for it to operate. The energy efficiency of this headset is therefore improved.

[0056] [Fig.2] represents a first embodiment of the device 1 which has just been described in general.

[0057] According to this first embodiment and as illustrated in [Fig.2], the transmitter 10 is an array (or matrix) of identical elementary ultrasonic transducers 100 of the micromachined piezoelectric type also called PMUTs for “Piezoelectric Micromachined Ultrasonic Transducers” in English. Such arrays offer the advantage of being convenient to manufacture in high density and allow, thanks to the micrometric dimensions of the PMUTs, to generate a complex haptic effect. The expression “complex haptic effect” designates a haptic effect which is produced, for example, in three dimensions, or at several target points.

[0058] In this configuration, each PMUT 100 of the transmitter 10 is then configured to emit a portion of the forward ultrasonic waves 01 and a portion of the rear ultrasonic waves 02 by a direct piezoelectric effect triggered under the effect of the supplied power Pem and a control signal.

[0059] Each PMUT 100 of the emitter 10 may have a diameter of between 30 pm and 1500 pm, for example a diameter equal to 800 pm.

[0060] The resonant frequency of the transmitter 10 is, in this first embodiment, determined by the resonant frequency of each PMUT 100 which composes it. Each PMUT 100 of the transmitter 10 has a resonant frequency greater than 40 kHz so as to generate the ultrasonic waves O1 and O2. In this example, each PMUT 100 of the transmitter 10 has a resonant frequency equal to 100 kHz.

[0061] The PMUTs are arranged with the same first repetition step along the OX axis and with the same second repetition step along the OY axis.

[0062] This second repetition step may or may not be equal to the first repetition step.

[0063] For example, the first and second repetition steps may be equal to 1100 pm when the diameter of each PMUT is 800 pm.

[0064] [Fig.4] represents measurement results giving the acoustic pressure, measured in pascals (or Pa), generated by a single PMUT 100 of the transmitter 10 as a function of the distance to this PMUT. For these measurements, the PMUT 100 is supplied with a voltage of 5 V and has a resonance frequency of 100 kHz.

[0065] As shown in [Fig.4], an acoustic pressure of 0.15 Pa is measured at a distance of 30 cm from the transmitter 10.

[0066] The supply voltage applied to the transmitter 10 (therefore to the network of PMUTs forming the transmitter 10) is preferably 48 V. Thus, the acoustic pressure produced at a distance of 30 cm from a PMUT of the transmitter is estimated at 1.44 Pa.

[0067] The number of PMUT 100 of the transmitter 10 may furthermore be greater than 100, for example equal to 139.

[0068] Thus, for 139 PMUTs and a supply voltage of the transmitter 10 set at 48 V, the acoustic pressure produced at a distance of 30 cm from the transmitter 10 by all the PMUTs 100 of the transmitter 10 is strictly greater than 200 Pa, i.e. above the threshold producing the illusion of touch on human skin.

[0069] The surface area occupied by all the PMUTs 100 of the transmitter 10, hereinafter called “active surface area”, may be greater than 1 cm x 1 cm, for example equal to 1.5 cm x 1.5 cm. Thus, the device 1 may be easily integrated into systems worn by the user, where space constraints are significant, while maintaining a sufficient density of PMUTs to create a complex haptic effect.

[0070] Still according to this first embodiment, and as illustrated by [Fig.2], the receiver 20 is also a network of PMUTs 200.

[0071] Each PMUT 200 of the receiver 20 is then configured to receive and convert by an inverse piezoelectric effect a portion of the rear ultrasonic waves 02 into an elementary current. Each elementary current contributes to forming the current irec produced by the receiver 20.

[0072] The use of an array of PMUTs as receiver 20 makes it possible to provide a large reception surface for the rear ultrasonic waves 02, and therefore to increase the sensitivity of detection and conversion of these waves. More generally, the use of arrays of PMUTs for the transmitter 10 and the receiver 20 makes it possible to obtain a device 1 that is both more efficient (the haptic effect generated is more complex) and more energy-efficient (a greater quantity of energy is recovered).

[0073] In [Fig.2], the network 20 of PMUTs 200 forming the receiver 20 is here identical to the network 10 of PMUTs 100 forming the transmitter 10 in that 1) the number of PMUTs 200 is identical to the number of PMUTs 100 of the transmitter 10, 2) the diameter of each of its PMUTs 200 is identical to that of each PMUT 100 of the transmitter 10, and 3) in that its PMUTs 200 are arranged in the same way (with the same repetition steps) along the OX and OY axes.

[0074] It is noted that then each PMUT 200 of the transmitter 20 is preferably arranged opposite one of the PMUTs 100 of the transmitter 10.

[0075] Concretely, each PMUT 200 of the receiver is stacked under (at the rear) of the PMUT 100 of the corresponding transmitter.

[0076] [Fig. 3] shows a sectional view of such a stack (denoted CTR in Figures 2 and 3). This has a cylindrical shape, according in this example to the same longitudinal axis RR' parallel to the axis OZ.

[0077] As shown in [Fig.3], the PMUT 100 of the transmitter and the PMUT 200 of the corresponding receiver are identical in their structure and dimensions (diameter, height). In particular, they comprise the same elements here and have the same design.

[0078] In a known manner, each PMUT 100, 200 of this CTR stack comprises a circular vibrating membrane, a membrane support which supports the vibrating membrane and a cavity arranged under (or at the rear) of the vibrating membrane.

[0079] In [Fig.3], the vibrating membrane, the membrane support and the cavity of the PMUT 100 of the transmitter 10 are referenced respectively with the numbers 101, 102 and 103. The vibrating membrane, the membrane support and the cavity of the PMUT 200 of the receiver 20 are referenced respectively with the numbers 201, 202 and 203.

[0080] The vibrating membrane 101 of the transmitter 10 is here configured to resonate at a frequency equal to the desired frequency for the transmitter 10 (therefore for example a frequency of 100 kHz) and to generate an acoustic pressure of 1.44 Pa when this transmitter 10 is supplied with a control voltage of 48 V.

[0081] In the example of [Fig. 3], the vibrating membrane 201 of the receiver 20 has the same thickness (in addition to the same diameter) as the thickness of the PMUT 100 of the transmitter 10. The vibrating membrane 201 of the receiver 20 is therefore configured to resonate at the same resonant frequency as the resonant frequency of the PMUT 100 of the transmitter 10 (therefore here 100 kHz). Thus, in use, the rear ultrasonic wave 02 coming from the transmitter 10 can put the membrane 201 of the PMUT 200 of the receiver 20 into resonance. At the resonant frequency, the deformation of the membrane 201 is the greatest, and therefore the recovery of the current irec is the greatest.

[0082] Naturally, the vibrating membrane 201 of the receiver 20 may alternatively have a configuration different from that of the PMUT 100 of the transmitter 10. In particular, the thickness and / or the constituent materials of the vibrating membrane 201 of the PMUT 200 of the receiver 20 may be respectively different from the thickness and / or the constituent materials of the vibrating membrane 101 of the PMUT 100 of the transmitter 10. In such a configuration, the rear ultrasonic waves 02 have a frequency different from the resonance frequency of the PMUTs 201 of the receiver 20. These rear ultrasonic waves 02 consequently cause a lower mobility of the vibrating membrane 201 of each PMUT 200 of the receiver, and therefore a lower recovered irec current, compared to the case where these rear ultrasonic waves 02 have a frequency substantially equal to the resonance frequency of the PMUTs 200 of receiver 20.In return, the vibrating membranes 201 of each PMUT 200 of the receiver 20, because they are less mobile, attenuate the rear ultrasonic waves 02. The receiver 20 then acts as a protective rear layer, since it makes it possible to reduce the acoustic pressure produced at the rear of the device 1. It is then possible to reduce the distance between the device 1 and the user U when this device 1 is intended to be fixed on this user U.

[0083] In any event, even when each PMUT 100 of the transmitter 10 has a resonance frequency substantially equal to the resonance frequency of the PMUTs 200 of the receiver 20, the rear ultrasonic waves 02 are in practice attenuated when they pass through the receiver 20 (losses necessarily occur in practice through the receiver 20). This allows the receiver 20 to produce both an energy harvesting effect and an attenuation of the ultrasonic waves 02 generated by the transmitter 10 and propagating in the second direction D2. This thus makes it possible to obtain a haptic device 1 that is more energy efficient than the haptic devices of the prior art, and more suitable for being fixed on a user (since the distance between this user and the haptic device 1 can be reduced without causing danger to the user).

[0084] The vibrating membrane 101, 201 of each PMUT 100, 200 shown in [Fig. 3] is a multi-layer structure: it comprises successively, from the bottom of the corresponding cavity towards the top (or the front, in [Fig. 3]), an inert layer forming a membrane and a piezoelectric pattern configured to actuate (make vibrate) the inert layer above the corresponding cavity.

[0085] The inert layer may be a single-layer structure or, as shown in [Fig. 3], a multi-layer structure formed, for example, from a first layer of polycrystalline silicon and a second layer of oxide.

[0086] In [Fig. 3], the polycrystalline silicon layer and the oxide layer forming the inert layer of the vibrating membrane of the PMUT 100 of the transmitter 10 are respectively denoted 1011 and 1013. The piezoelectric pattern of the PMUT 100 of the transmitter 10 is denoted 1012. The polycrystalline silicon layer and the oxide layer forming the inert layer of the membrane of the PMUT 200 of the receiver 20 are respectively denoted 2011 and 2013 and the piezoelectric pattern of the PMUT 200 of the receiver 20 is denoted 2012.

[0087] In the example of [Fig. 3], the piezoelectric pattern of each PMUT 100, 200 is here formed of a lower electrode pattern arranged on the vibrating membrane, an upper electrode pattern and a pattern of a piezoelectric material arranged between the lower electrode pattern and the upper electrode pattern. Finally, the piezoelectric pattern may also comprise a metal pattern arranged on the upper electrode pattern.

[0088] In [Fig. 3], the lower electrode pattern, the piezoelectric material pattern, the upper electrode pattern and the metal pattern of the PMUT 100 of the transmitter 10 are denoted with the respective references 1012-1, 1012-2, 1012-3 and 1012-4. The lower electrode pattern, the piezoelectric material pattern, the upper electrode pattern and the metal pattern of the PMUT 200 of the receiver 200 are denoted with the respective references 2012-1, 2012-2, 2012-3 and 2012-4.

[0089] The distance hiO_2o between the PMUT 100 of the transmitter 10 and the PMUT 200 of the receiver 20 is here defined by the height measured between the rear face 101b of the vibrating membrane 101 of the PMUT 100 of the transmitter 10 and the front face 201a of the membrane 201 of the PMUT 200 of the receiver 20. This distance hio_2o determines the distance between the transmitter 10 and the receiver 20, and is preferably between 400 pm and 1000 pm, preferably equal to 500 pm.

[0090] The distance hiO_2o thus specified is the minimum distance between the transmitter 10 and the receiver 20 compatible with the technological manufacturing constraints commonly used in semiconductor technologies (in particular those concerning the assembly, or the transfer, of substrates). This allows the device 1 to be effectively manufactured, and for it to have an improved energy harvesting capacity (the smaller the distance hiO_2o, the less the rear ultrasonic waves 02 are attenuated when they arrive at the receiver 20 and the greater the energy harvesting).

[0091] The power P, expressed in Pascal Pa, produced by a PMUT 100 of the transmitter 10 can be estimated using the formula (Fl) detailed below.

[0092] [Maths 1] (Fl)

[0093] ^.pS. ef P — r

[0094] Where: • P is the air density in Kg / m1 present on the surface of the membrane of the PMUT considered, • S is the surface area in m2 of the membrane of the PMUT considered, • £ is the amplitude in m of the vibration produced by the PMUT membrane, • f is the vibration frequency in Hz of the membrane of the PMUT considered, and • r is the distance in m to the PMUT membrane.

[0095] For a PMUT 100 of the transmitter 10 considered in the preceding paragraphs and r = 0.0001 ni, we can calculate an acoustic pressure P^ of the order of 700 Pa at the surface 101a of the vibrating membrane 101 of the PMUT 100 of the transmitter 10.

[0096] As the two membranes 101 and 102 of the PMUT 100 of the transmitter and of the PMUT 200 of the receiver 20 are stacked on top of each other and are here separated by hiO_2o equal to 500 pm, an acoustic pressure P20 on the membrane 201 of the receiver 10 of the order of 140 Pa is calculated, therefore lower by a factor of 5 than that generated on the membrane 101 of the PMUT 100 of the transmitter 10.

[0097] The acoustic pressure arriving at the membrane 201 of the receiver 20 deforms the latter 5 times less than the deformation of the membrane having generated this acoustic pressure. By direct piezoelectric effect, it can thus be estimated that it is possible recover, using the receiver 20, approximately 20% of the energy that was used to actuation the transmitter 10. Note that this is only an order of magnitude and that the energy recovery can be optimized by minimizing the distance hiO 2o between the membranes 101 and 102 of the PMUT 100 of the transmitter and the PMUT 200 of the receiver 20.

[0098] Naturally, the receiver 20 may be, in other embodiments, an array of PMUTs 200 having a different configuration from that of the array of PMUTs 100 forming the transmitter 10: for example, the number of PMUTs 200 may be different and / or the diameter of each PMUT 200 of the receiver 20 may be greater than the diameter of the corresponding PMUT 100 of the transmitter 10 (in this case, each PMUT 200 of the receiver may be actuated by several PMUTs 100 of the transmitter 10).

[0099] A second embodiment is represented in schematic form by [Fig.5],

[0100] According to this second embodiment, the device 1 further comprises a protective layer 40.

[0101] As shown in [Fig.5], the protective layer 40 is arranged behind the receiver 20, and preferably against this receiver 20. The receiver 20 is then arranged between the transmitter 10 and the protective layer 40.

[0102] The protective layer 40 is an inert layer (as opposed to the emitter 10 and the receiver 20 which are transducers, therefore active layers) formed from a metamaterial or any other material having an acoustic impedance capable of absorbing the ultrasonic waves propagating in the second direction D2.

[0103] More specifically, the protective layer 40 is configured to attenuate the amplitude of the rear ultrasonic waves 02, 03 to a level that does not produce dangerous effects for the user. Ideally, the protective layer 40 is configured to completely block the acoustic pressure generated by the rear ultrasonic waves. At a minimum, the protective layer 40 is configured to allow an acoustic pressure of a few tens of Pascals to pass through, preferably a few Pascals, for example 5 Pa.

[0104] In other words, the protective layer 40 is an inert layer configured so that the acoustic pressure produced by the ultrasonic waves transmitted through this protective layer 40 is strictly lower than the threshold above which a haptic effect is produced.

[0105] The transmitted ultrasonic waves concerned are the rear ultrasonic waves 02 having passed through the receiver 20 and / or the ultrasonic waves 03 having been generated by this receiver 20. In practice, in fact, the vibration of the membrane 201 of each PMUT 200 of the receiver 20 induces a generation of ultrasonic waves 03 towards the rear, therefore towards the user U. It is noted that the higher the frequency of the rear ultrasonic waves 02 (and therefore the resonance frequency of the PMUT 100 of the transmitter 10) is close to the resonant frequency of each PMUT 200 of the receiver 20, the less the rear ultrasonic waves 02 are attenuated, since the corresponding vibrating membrane 201 is made more mobile.

[0106] The second embodiment illustrated in [Fig.5] is compatible with the first embodiment, as illustrated in [Fig.6].

[0107] [Fig.6] thus shows a sectional view of the CTR stack shown in the [Fig.3] when the protective layer 40 is present. The protective layer 40 is disposed against the rear face 202b of the membrane support 202 of the PMUT 200 of the receiver 20.

[0108] This second embodiment is particularly advantageous when the device 1 is intended to be worn on the head of the user U. Indeed, the protective layer 40 makes it possible to ensure that the residual ultrasonic waves propagating at the rear of the device 1, therefore towards the user U, are not harmful to this user. This avoids having to move the device 1 away from the user U in order to comply with the safety conditions of the user U.

[0109] A manufacturing method in accordance with the invention, making it possible to manufacture the device 1 illustrated in [Fig.2] is described below.

[0110] [Fig.7] represents, in the form of a flowchart, the main stages of the process manufacturing (also referred to as “process” hereinafter).

[0111] As shown in [Fig.7], the method comprises the steps of: • SI manufacturing of transmitter 10, • S2 manufacturing of receiver 20, • Assembly S3 of the transmitter 10 and the receiver 20 such that in use the ultrasonic waves received and converted by the receiver 20 are the ultrasonic waves 02 generated by the transmitter propagating in the second direction, • Supply S4 of the energy recovery unit 30, and • Implementation S5 of the electrical connection between the energy recovery unit 30 and the receiver 20.

[0112] Figures 8A to 8J represent in sectional view sub-steps of step S1 of manufacturing the transmitter 10. It is recalled that this transmitter 10 is constituted by a network of PMUTs 100.

[0113] During sub-step S10, illustrated in [Fig.8A], a substrate 80 is provided. This substrate 80 is for example a silicon substrate, derived from a silicon wafer.

[0114] During sub-step SI 1, illustrated in [Fig.8B], an upper oxide layer 81 is deposited on the front face 80a of the substrate 80 and a lower oxide layer 82 is deposited on the rear face 80b of the substrate 80. These upper oxide layers and lower 81, 82 are intended to form, with the substrate 80, a membrane support common to all the PMUTs 100 of the emitter 10.

[0115] In sub-step S12, illustrated in [Fig.8C], an etching of the lower oxide layer 82 is carried out until reaching the rear face 10b of the substrate 80 so as to create an initial cavity 83.

[0116] During sub-step S13 illustrated in [Fig.8D], a polycrystalline silicon membrane 84 is deposited on the upper oxide layer 81 (thus forming the inert layer of the vibrating membrane 101 of the PMUTs 100), at the bottom of the initial cavity 83 and on the rear face of the lower oxide layer 82. The deposition of the membrane 84 can then be carried out according to a polycrystalline silicon growth technique on the upper oxide layer 81, at the bottom of the initial cavity 83 and on the rear face of the lower oxide layer 82.

[0117] The polymer membrane 84 deposited on the upper face of the upper oxide layer 81 forms the inert layer 1011 of a vibrating membrane 101 common to all the PMUTs 100 of the transmitter 10.

[0118] According to a variant, the membrane 84 can be formed from several layers deposited successively on the first substrate 80, including a layer of silicon oxide, for example 1.9 μm thick, and polysilicon (for example 4 μm thick). Other materials can alternatively be envisaged, based on monocrystalline silicon, or silicon nitride.

[0119] Then, in sub-steps S14 to S18, shown respectively in FIGS. 8E, 8F, 8G, 8H and 8I, the piezoelectric pattern 1012 of each PMUT 100 of the emitter 10 is formed.

[0120] In sub-step S14 illustrated in [Fig.8E], a lower metal layer 86 of the material of the lower electrode pattern 1012-1 (of each piezoelectric pattern) is deposited on the upper oxide layer 85 using a full-plate deposition technique. The upper metal layer 86 is for example formed of platinum or Pt and has a thickness of 100 nm.

[0121] Then, in sub-step S15 illustrated in [Fig.8F], a layer 87 of the material of the piezoelectric pattern 1012-2 is formed on the lower metal layer 86, according to a full-plate deposition technique. The piezoelectric material can be chosen (in a non-limiting manner) from the following materials: lead zirconate titanoate PZT, aluminum nitride or AIN, zinc oxide or ZnO. The thickness of the layer 87 of the material of the piezoelectric pattern 1012-2 can be 2 μm.

[0122] In sub-step S16 illustrated in [Fig.8G], an upper metal layer 88 of the material of the upper electrode pattern 1012-3 is deposited on the layer 87 of the material of the piezoelectric pattern 1012-2. The upper metal layer 88 can be formed of a lower sub-layer based on ruthenium (Ru) with a thickness of 100 nm and an upper sub-layer based on gold (Au) with a thickness of 500 nm.

[0123] A first etching is then carried out, during sub-step S17 illustrated in [Fig.8H], through the upper metal layer 88 and a second etching is carried out through the layer 87 of the material of the piezoelectric pattern 1012-2 until reaching the lower metal layer 86, so as to create initial piezoelectric patterns 88 from which the final piezoelectric patterns 1012 will be formed.

[0124] During sub-step S18, illustrated in [Fig.81], a third etching is carried out between the initial piezoelectric patterns 88 and through the lower metal layer 86 until reaching the membrane 84, so as to form the final piezoelectric patterns 1012 of each PMUT 100 of the emitter 10.

[0125] Finally, during sub-step S19, illustrated in [Fig.8J], an etching is carried out through the lower oxide layer 82 accessible from the initial cavity 83, until reaching the membrane 84. Thus, the cavity of each PMUT is formed under the membrane 84.

[0126] According to a variant, sub-step S19 is not carried out. Thus, the membrane of the PMUT 100 is formed from the polycrystalline silicon layer 84 and the lower and upper oxide layer 82, 81.

[0127] Step S2 of manufacturing the receiver 20 is identical to step S1 in that it comprises the same sub-steps.

Claims

Claims

1. Haptic device (1) of remote type comprising a first transducer (10) called transmitter (10) configured to generate, under the effect of a control signal (ie), ultrasonic waves (01, 02) reproducing the illusion of touch on human skin, a part (01) of the ultrasonic waves (01, 02) propagating in a first direction (Dl) going from the transmitter (10) to a target area (C) located at a distance from the haptic device (1) and another part (02) of the ultrasonic waves (01, 02) propagating in a second direction (D2) opposite to the first direction (Dl), said haptic device (1) being characterized in that it further comprises: - A second transducer (20) called receiver (20), configured to receive and convert into an electric current (irec) the ultrasonic waves (02) propagating in the second direction (D2), the transmitter (10) being arranged between the target area (C) and the receiver (20),- An energy recovery unit (30) electrically connected to the receiver (20) and configured to receive the electric current (irec) produced by the receiver (20).,

2. A haptic device (1) according to claim 1, wherein the receiver (20) is a transducer of the same type as the transmitter (10), the type being for example a piezoelectric transducer or a magnetostriction transducer.

3. Haptic device (1) according to claim 1 or 2, wherein the receiver (20) has a resonant frequency equal to a resonant frequency of the transmitter (10) plus or minus 500 Hz, preferably equal to a resonant frequency of the transmitter (10) plus or minus 50 Hz.

4. Haptic device (1) according to claim 3, wherein said resonant frequency is greater than or equal to 20 kHz, preferably equal to 100 kHz.

5. Haptic device (1) according to one of claims 1 to 4, wherein the receiver (20) is separated from the transmitter (10) by a distance (hw 20) less than or equal to 1000 pm, preferably less than or equal to 800 pm, preferably less than or equal to 500 pm, said distance (hio-20) being measured along the second direction (D2) between a rear face (10b) of the transmitter and a front face (20a) of the receiver (20).

6. Haptic device (1) according to one of claims 1 to 5, wherein the energy recovery unit (30) is electrically connected to the transmitter (10) and configured to inject the electric current (irec) produced by the receiver (20) into the transmitter (10), said electric current (irec) being used to produce at least in part the control signal (ie) of the transmitter (10).

7. Haptic device (1) according to one of claims 1 to 5, wherein the energy recovery unit (30) is electrically connected to an output track (32) of the haptic device (1), the output track (32) being intended to be electrically coupled to a power supply unit external to the haptic device.

8. Haptic device (1) according to one of claims 1 to 7, wherein the haptic device (1) further comprises a protective layer (40) configured to attenuate the ultrasonic waves (02, 03) propagating in the second direction, the receiver (20) being arranged between the transmitter (10) and the protective layer (40).

9. Haptic device (1) according to one of claims 1 to 8, in which the transmitter (10) is an array of elementary transducers and the receiver is also an array of elementary transducers, each elementary transducer of the receiver being arranged opposite at least one of the elementary transducers of the transmitter.

10. Haptic device (1) according to claim 9, in which the array of elementary transducers forming the receiver has the same number of elementary transducers as the array of elementary transducers forming the transmitter, said number of elementary transducers being greater than 100, for example equal to 139.

11. Haptic device (1) according to one of claims 9 or 10, in which the network of elementary transducers forming the receiver has, in top view, a shape identical to a shape of the network of elementary transducers forming the transmitter, said shape having two lateral dimensions, each lateral dimension being greater than or equal to 2 cm, preferably greater than or equal to 1 cm.

12. Haptic device (1) according to one of claims 9 to 11, in which each elementary transducer is a transducer

13. micro-machined piezoelectric ultrasonic also called PMUT, the network of elementary transducers then being a network of micro-machined piezoelectric ultrasonic transducers also called PMUT network. Method for manufacturing a remote type haptic device according to one of claims 1 to 12 comprising the steps of: - Manufacture (SI) of the transmitter (10), - Manufacture (S2) of the receiver (20), - Assembly (S3) of the transmitter (10) and the receiver (20) such that in use the ultrasonic waves received and converted by the receiver (20) are the ultrasonic waves (02) generated by the transmitter (10) propagating in the second direction (D2), - Supply (S4) of the energy recovery unit (30), - Production (S5) of the electrical connection between the energy recovery unit (30) and the receiver (20).