WO2021094587A1

WO2021094587A1 - Spin-wave based magnetic and/or electro-magnetic field sensing device for dc, rf and millimeter-wave applications

Info

Publication number: WO2021094587A1
Application number: PCT/EP2020/082141
Authority: WO
Inventors: Sidina Wane; Quang Hung Tran
Original assignee: eV-Technologies
Priority date: 2019-11-13
Filing date: 2020-11-13
Publication date: 2021-05-20
Also published as: EP4085266A1

Abstract

The present disclosure relates to a sensing device for sensing magnetic and/or electro-magnetic fields comprising a first sensing module comprising: a first tier comprising an integrated circuit chip implementing at least an amplifier; and a second tier positioned over the first tier, the second tier comprising a spin-wave sensor having at least first and second connection nodes, wherein the first connection node of the spin-wave sensor is coupled to a first input of the amplifier.

Description

DESCRIPTION

Spin-Wave based Magnetic and/or Electro-magnetic Field Sensing Device for DC, RF and Millimeter-Wave Applications

[0001] The present patent application claims priority from the French patent application filed on 13 November 2019 and assigned application no. FR1912654, the contents of which is hereby incorporated by reference in its entirety.

Technical field

[0002] The present disclosure relates generally to the field of magnetic field and/or electro-magnetic field sensors, and in particular to a sensing device for DC (Direct Current), RF (Radio Frequency) and millimeter-wave applications.

Background art

[0003] The automatized testing and validation of 5G (Fifth Generation) and IoT (Internet of Things) communication devices requires appropriate instruments capable, for example, of evaluating power integrity (PI), signal integrity (SI), and conformity with EMC (Electro-Magnetic Capability) and EMI (Electro-Magnetic Interference) specifications. Indeed, PI, SI, EMC and EMI performance is a critical issue for new generation communications systems that are required to have very high data transmission rates, low energy consummation, and a strong immunity to undesirable disturbances.

[0004] Sensor technologies have been proposed based on quantic interferences in superconductors, such as the magnetometer known in the art as Quantum SQUID

(Superconducting Quantum Interference Device). Such technologies are extremely sensitive, but have the disadvantage of being required to operate at very low temperatures of a few tens of degrees Kelvin. [0005] There is thus a need in the art for a solution for magnetic and/or electro-magnetic field sensing with relatively high precise in an industrial setting.

Summary of Invention

[0006] It is an aim of embodiments of the present disclosure to at least partially addresses one or more needs in the prior art.

[0007] According to one aspect, there is provided A sensing device for sensing magnetic and/or electro-magnetic fields comprising a first sensing module comprising: a first tier comprising an integrated circuit chip implementing at least an amplifier; and a second tier positioned over the first tier, the second tier comprising a spin-wave sensor having at least first and second connection nodes, wherein the first connection node of the spin-wave sensor is coupled to a first input of the amplifier.

[0008] According to one embodiment, the amplifier is a differential amplifier, and a second connection node of the spin-wave sensor is coupled to a second input of the amplifier

[0009] According to one embodiment, the spin-wave sensor further comprises third and fourth connections nodes, and the integrated circuit chip further comprises a regulator configured to apply a voltage or current across the third and fourth connection nodes.

[0010] According to one embodiment, the spin-wave sensor has a multi-layer structure comprising a ferromagnetic layer and an antiferromagnetic layer.

[0011] According to one embodiment, the multi-layer structure further comprises a non-magnetic layer, for example of copper, between the ferromagnetic and antiferromagnetic layers. [0012] According to one embodiment, the sensing device further comprises a substrate on which the first tier is positioned .

[0013] According to one embodiment, the spin-wave sensor comprises a plurality of contact pads coupled to the integrated circuit chip via wire bonding and/or via a plurality of micro bumps.

[0014] According to one embodiment, the first sensing module is in the form of a package comprising a mounting surface for mounting the package to a substrate, wherein the mounting surface comprises a plurality of micro-bumps for providing electrical connections to the substrate.

[0015] According to one embodiment, the sensing device further comprises a further substrate on which the first sensing module is mounted.

[0016] According to one embodiment, the further substrate comprises a shielding layer formed of a metal, and wherein input/output terminals of the first sensing module are coupled to a via passing through an opening in the shielding layer.

[0017] According to one embodiment, the sensing device further comprises a second sensing module mounted on the substrate, wherein the first and second sensing modules are oriented so as to receive signals of opposite polarizations to each other.

[0018] According to one embodiment, the sensing device comprises a sensor network formed of a 1-dimensional, 2- dimensional or 3-dimensional array of pixels, each pixel comprising the first and second sensing modules.

[0019] According to one embodiment, the sensor network is mounted on a near-field scanning system configured to displace the sensor network by steps of fixed length in each of one or more directions, where the fixed length in each direction is less than the pixel pitch in that direction.

[0020] According to a further aspect, there is provided a test system comprising: the above sensing device; and a control board coupled to the sensing device, the control board comprising at least two mixers configured to down-convert the frequencies of signals received by one or more of the sensing modules into digital signals; and at least two analog to digital converters configured to convert the down-converted signals into digital signals.

Brief description of drawings

[0021] The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0022] Figure 1 illustrates a multi-layer structure of a spin-wave sensor according to an example embodiment of the present disclosure;

[0023] Figure 2 is a graph illustrating a voltage profile as a function of magnetic field for two different spin-wave structures;

[0024] Figure 3 illustrates examples of detection coils of a spin-wave sensor;

[0025] Figure 4 illustrates a sensing module comprising a spin-wave sensor and an integrated circuit according to an example embodiment of the present disclosure;

[0026] Figure 5 is a top view of the sensing module of Figure 4 according to an example embodiment of the present disclosure; [0027] Figure 6A schematically illustrates a spin-wave sensor according to an example in which it is referenced to ground;

[0028] Figure 6B schematically illustrates a spin-wave sensor according to an example in which it is biased by a DC voltage;

[0029] Figure 7 illustrates an assembly of a sensing module and a circuit board by wire bonding according to an example embodiment of the present disclosure;

[0030] Figure 8 illustrates a flip-chip assembly of a sensing module and a circuit board according to an example embodiment of the present disclosure;

[0031] Figure 9 schematically illustrates the sensing module of Figure 4 in more detail according to an example embodiment of the present disclosure;

[0032] Figure 10A is a cross-section view of the sensor module of Figure 4 based on a wire bonding assembly;

[0033] Figure 10B is a cross-section view of the sensor module of Figure 4 based on a 3D-interconnect assembly;

[0034] Figure 11 is a perspective view of a probe comprising a sensing module according to an example embodiment of the present disclosure;

[0035] Figure 12 schematically illustrates a probe array according to an example embodiment of the present disclosure;

[0036] Figure 13 schematically illustrates a pair of probing elements according to an example embodiment;

[0037] Figure 14 is a plan view of a near-field scanning system configured to displace a probe array in two dimensions;

[0038] Figure 15 schematically illustrates a system comprising the probe array and a control board according to an example embodiment of the present disclosure; [0039] Figure 16 schematically illustrates a sensing device comprising pixels according to an example embodiment of the present disclosure; and

[0040] Figure 17 schematically illustrates a readout circuit for a probe array according to an example embodiment of the present disclosure.

Description of embodiments

[0041] Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.

[0042] Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements .

[0043] In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or to relative positional qualifiers, such as the terms "above", "below", "higher", "lower", etc., or to qualifiers of orientation, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures, or to a magnetic field sensing device as orientated during normal use.

[0044] Unless specified otherwise, the expressions "around", "approximately", "substantially" and "in the order of" signify within 10 %, and preferably within 5 %. [0045] Figure 1 illustrates a multi-layer structure 100 of a spin-wave sensor according to an example embodiment of the present disclosure. As known by those skilled in the art, a spin-wave sensor, also known as a spin-electronic sensor, Hall-sensor, or magnetic AMR/PHR (Anisotropic Magneto- Resistance/Planar Hall Resistance), is a sensor that is sensitive to magnetic fields. For example, such a device is described in more detail in the European patent application published as EP3208627 by F.TERKI et al. entitled "Measurement system and method for characterizing at least one single magnetic object", the contents of which is hereby incorporated by reference.

[0046] With reference to Figure 1, the structure of the spin- wave sensor for example comprises a capping (not illustrated), an antiferromagnetic (AFM) layer 102, a spacer 104, for example formed of a non-magnetic material such as copper, and having a thickness t, a ferromagnetic (EM) layer 106, a seed layer (not illustrated) , and a substrate (also not illustrated) . The ferromagnetic layer 106 is for example formed of NiFe or CoFe. The spacer 104 is optional, and for example has the advantage of increasing the sensitivity of the sensor, as will be described below with reference to Figure 2. In the structure of Figure 1, a relatively strong coupling (represented by a dashed line 108) between the AFM layer 102 and the FM layer 106 allows a reduction in the hysteresis of the sensor. Such a three-layer thin film structure is for example favorable for the detection of low frequency electromagnetic fields, whereas a strong coupling between the FM and AFM layer 102, 106 is for example preferable for the detection of high frequency electromagnetic fields.

[0047] Figure 2 is a graph illustrating a voltage profile as a function of magnetic field for two different spin-wave structures. A curve 202 is based on the structure 100 of Figure 1, but without the spacer 104, i.e. t=0 run. A curve 204 is based on the structure 100 of Figure 1 with a spacer thickness t of 0.12 nm. It can be seen that the slope of the response, and thus the sensitivity of the sensor, is higher for structure with spacer.

[0048] According to one example, a bi-layer structure comprises an AFM layer 102 of IrMn having a thickness of between 5 and 20 nm, and for example of 10 nm, and an FM layer 106 of NiFe having a thickness of between 2 and 6 nm, and for example of 4 nm. According to another example, a tri-layer structure comprises an AFM layer 102 of IrMn having a thickness of between 5 and 20 nm, and for example of 10 nm, a spacer layer formed of Cu having a thickness of between 0.1 and 0.4 nm, and for example of 0.2 nm, and an FM layer 106 of NiFe having a thickness of between 5 and 20 nm, and for example of 10 nm.

[0049] The architecture of a spin-wave sensor based on a multi-layer structure as described in relation with Figure 1 may be single loop, or may comprises several closed loops, as will now be described in more detail with reference to Figure

3.

[0050] Figure 3 illustrates, in plan view, examples of detection loops of a spin-wave sensor. Four examples are based on open loops 302, and a further nine examples are based on closed loops 304.

[0051] Each of the open loops 302 comprises a terminal 310 coupled by a relatively short link to one end of the detection loop, and another terminal 312 coupled by another relatively short link to the other end of the detection loop. The detection loop of each of the open loops is for example substantially circular with an opening at the terminals 310, 312. The radius rl of these detection loops is for example in the micronic to millimeter range, depending on the frequency range to be detected. A width W of the trace forming the detection loop is for example in the micronic to millimeter range. A further open or closed inner loop may be present, or the detection loop layer have a more complex pattern such that it forms both outer, inner and intermediate loops.

[0052] Each of the closed loops 304 for example comprises four terminals 330, 332, 334 and 336 at north, east, south and west sides of the detection loop. In some case the closed loop is substantially circular, and the terminals 330, 332,

334 and 336 are connected by short links to corresponding points around the loop. The radius of these detection loops, and the width of the trace forming these loops, is for example the same as for the examples of the open loops. There may additionally be one or more inner loops. Furthermore, rather than circular detection loops, some of the examples are based on diamond-shaped closed loops, and one example is based on a square arrangement of meanders. A width of each of these diamond and square detection loops is for example substantially equal to the diameters of the circular detection loops .

[0053] Figure 4 illustrates a sensing module 400 comprising a spin-wave sensor 402 and an integrated circuit according to an example embodiment of the present disclosure. The example of Figure 4 is based on a closed detection loop having four terminals as described above with reference to the examples 304 of Figure 3. However, it will be apparent to those skilled in the art that it would be possible to replace the closed detection loop by an open detection loop having just two terminals . [0054] The spin-wave sensor 402, and its connection terminals 330, 332, 334, 336, are for example formed in a top tier of the device. Furthermore, as schematically represented by components on the side of the module 400 in Figure 4, circuits such as an amplifier and voltage regulator are for example implemented by an integrated circuit 404 that is assembled with the sensor 402. For example, the sensor module 400 is a package comprising an embedded integrated circuit 404. For example, in some embodiments, the package uses SESUB (Semiconductor Embedded in a Substrate) technology. The integrated circuit 404 is for example mounted on a substrate 406, which is some embodiments could be a flexible substrate.

[0055] Figure 5 is a top view of the sensing module 400 of Figure 4 according to an example embodiment of the present disclosure. The sensing module 400 for example has a substantially square footprint, and width of between 1 and 10 mm, although other shapes and dimensions would be possible. In the example of Figure 5, the sensing module 400 has a width of around 2.5 mm. The example of Figure 5 is based on a spin- wave sensor 402 having a closed detection loop, and four contact pads corresponding to the terminals 330, 332, 334 and 334 of the closed detection loop are visible on the top surface of the sensing module 400, close to its respective corners .

[0056] Furthermore, the detection loop 402 of the sensing module 400 is visible, and Figure 5 illustrates one possible patterning of this detection loop. In particular, the loop 402 is for example formed over a square-shaped area which is positioned in the middle of the sensing module 400 orientated at an angle of 45 degrees with respect to the edges of the sensor. The detection loop 402 for example comprises, in each quadrant of its area, a serpentine pattern, adjacent quadrants having serpentines running perpendicular to each other, and diagonally opposing quadrants having serpentines running the same direction as each other. A point of the detection loop between each of the adjacent quadrants is connected to a corresponding one of the terminals 330, 332, 334 and 336. Of course, other patterns of the detection loop 402 would be possible, such as the one described in the patent application EP 3208627 referenced above or any of those described in relation with Figure 3.

[0057] Figure 6A schematically illustrates a spin-wave sensor 602 according to an example in which it is referenced to ground, in other words the terminals 332 and 336 being coupled to ground rails, and the terminals 330 and 334 providing an output signal (SIGNAL) of the sensor.

[0058] Figure 6B schematically illustrates a spin-wave sensor 604 according to an example in which it is biased by a DC biasing voltage, in other words the contacts 332 and 336 receiving a DC biasing voltage (DC BIAS), and the contacts 330 and 334 providing an output signal (SIGNAL) of the sensor.

[0059] Figure 7 illustrates a sensing device 700 formed of an assembly of the sensing module 400 and a circuit board 702 by wire bonding 704 according to an example embodiment of the present disclosure. The sensing module 400 is for example mounted on a surface of the board 702, which is for example a printed circuit board (PCB). The sensing module 400 for example comprises connection pads 706 on its upper surface, there being four in the example of Figure 7, and the circuit board 702 for example comprises corresponding connection pads 708 on its upper surface around the area in which the module 400 is mounted. A wire bond 704 for example connects each of the pads 706 to a corresponding one of the pads 708. A first pair of the pads 708 is for example connected, via routing within the circuit board 702, to contacts of a connector 710, which is for example an SMT (Surface Mount Termination) connector or an SMPM (Sub-Miniature Push-on Micro) connector. Similarly, a first pair of the pads 708 is for example connected, via routing within the circuit board 702, to contacts of a connector 712, which is also for example an SMT (Surface Mount Termination) connector or an SMPM (Sub- Miniature Push-on Micro) connector. The connectors 710, 712 are for example mounted on an underside of the circuit board 702, and the connections to the connectors 710, 712 for example traverse corresponding openings in a shielding layer (not illustrated) formed on or close to the underside of the circuit board 702.

[0060] Figure 8 illustrates a sensing device 800 formed by a flip-chip assembly of the sensing module 400 and the circuit board 702 according to an example embodiment of the present disclosure. The sensing device 800 is similar to that of Figure 7, except that the connection pads 706 on the module 400 are replaced by connection bumps 802, such as micro bumps, and the module 402 is flipped over and mounted on the circuit board 702 with the bumps 802 bonding to the corresponding pads 708 on the circuit board 702.

[0061] Figure 9 schematically illustrates the sensing module 400 of Figure 4 in more detail according to an example embodiment. A dashed rectangle 902 in Figure 9 represents a top surface of the sensing module 400 on which the connection pads 330, 332, 334 and 336 of the spin-wave sensor are for example coupled by wire bonding to corresponding pads 930, 932, 934 and 936 on the surface of the module 400, which are coupled, for example via internal routing, to the integrated circuit 404. The integrated circuit 404 for example comprises a voltage regulator (REG) 940 that receives, at an input terminal 942 of the sensing module 400, a DC supply voltage. The regulator 940 for example generates a DC biasing voltage (DC BIAS), which is applied to the connection pad 936. A further input terminal 944 of the sensing module 400 for example receives a ground voltage (GND), which is for example routed to the connection pad 932. The connection pads 930 and 934 are for example respectively routed to corresponding inputs of a differential amplifier 946. The amplifier 946 is for example supplied by a supply voltage that is also generated by the voltage regulator 940, and by a ground voltage via the ground rail coupled to the terminal 944. An output of the amplifier 946 is coupled to an output terminal 948 of the sensing module 400, which provides an output signal O/P SIGNAL of the module 400. While this output signal is shown as a single-ended output signal in the example of Figure 9, it would also be possible for this output signal to be a differential output signal provided on two terminals, such that the sensing module 400 has four input/output terminals, rather than just three.

[0062] In some embodiments, a further gain stage 950 is provided between the output of the amplifier 946 and the output terminal 948 of the sensing module 400. This further gain stage 950 is for example configured to automatically correct, using a trigger mechanism, a dynamic range of the sensed signal. For example, the gain stage 950 is supplied by the same voltage rails as the amplifier 946, and is controlled by a control line 952 from the amplifier 946. The control line 952 for example supplies a control signal indicating an operating point of the amplifier 946, thereby permitting appropriate amplification or attenuation to be applied by the gain stage 950 including control of hysteresis responses.

[0063] Figure 10A is a cross-section view of the sensor module 400 of Figure 4 based on a wire bonding assembly. The spin-wave sensor 402 is for example implemented in a top tier of the device, with the connection pads 930, 932, 934 and 936 for example being formed on a top surface of a substrate 1002 on which the spin-wave sensor 402 is mounted, and electrically connected by corresponding wire bonds. The substrate 1002 for example comprises internal routing 1030, 1032, 1034 and 1036 that connects each of the pads 930, 932, 934 and 936 respectively to a corresponding connection bump 1040 on an underside of the substrate 1002. For example, the internal routing 1030, 1032, 1034 and 1036 is formed by copper pillars and tracks.

[0064] The integrated circuit 404 is for example embedded in the structure between the substrate 1002 and a further substrate 1004. The connection bumps 1040 for example connect to corresponding connection pads (not illustrated) on a top surface of the integrated circuit 404. Connection bumps 1042, 1044 and 1048 are for example present on an underside of the integrated circuit 404, and for example connect the output terminals 942, 944 and 948 of the sensing module 400 to corresponding connection pads on the substrate 1004, which is for example a PCB. Two such pads 1052 and 1054 are illustrated in Figure 10A. The signals from the input/output terminals 942, 944 and 948 of the sensing module 400 are for example routed via internal connections of the substrate 1004 to an underside of the substrate 1004, where they are for example available to be connected to connectors or the like (not illustrated) .

[0065] Figure 10B is a cross-section view of the sensor module 400 of Figure 4 based on a 3D-interconnect assembly. The implementation is similar to that of Figure 10A, except that the connection pads 330, 332, 334 and 336 of the spin- wave sensor 402 are connected to the connection pads 930, 932, 934 and 936 of the substrate 1002 via a 3D-assembly comprising, for example, corresponding L-shaped pieces 1060, 1062, 1064 and 1066 that replace conventional bond-wiring connections. [0066] Figure 11 is a perspective view of a probe 1100 comprising the sensing device 700 or 800 of Figure 7 or 8, and a shielded cable 1102 linking the sensing device 700, 800 to a connector 1104, suitable for example for coupling to a measuring device such as an oscilloscope.

[0067] Figure 12 schematically illustrates a probe array 1200 comprising sensor modules 400, 400' according to an example embodiment of the present disclosure. The sensor modules 400' are the same as the modules 400, but orientated so as to receive signal of an opposite polarization that of the sensor modules 400. For example, the sensor modules 400 are configured to receive X-polarized signals, and the sensor modules 400' are configured to receive Y-polarized signals. The array 1200 comprises an 8 by 8 array of sensor modules 400 and 400'. More generally there could be q lines and r rows of sensor modules 400, 400', where q and r are from example each equal to at least two, and for example to at least four. In some embodiments, a probing device could however, comprise only a single pair of sensor modules 400, 400'.

[0068] As described above, the sensor modules for example comprise spin-wave sensors having four terminals. In some embodiments, among the four terminals, two diagonally opposite terminals form biasing contacts that are coupled to a ground voltage or to a biasing voltage, which is for example a DC biasing voltage, or a voltage signal having a relatively low frequency, such as in the kHz range or less. The remaining two diagonally opposite contacts form output nodes of the sensor that present an output signal in the form of a voltage difference that varies as a function of the detected magnetic field . [0069] The sensing modules 400 are for example arranged in a checker-board pattern with respect to the sensing modules 400'. In such a case, a diagonal separation DC between the modules 400, and the diagonal separation DU between the modules 400', are for example identical, and for example equal to between 1 mm and 20 mm, and for example to between 2 mm and 5 mm.

[0070] The sensing modules 400, 400' for example permit a correlation of DC and RF responses based on non-linearities of the probing array scanning system for an accurate extraction of parameters such as BER (bit error rate) and EVM as a function of frequency, modulation and data rate; spectral mask and flatness; occupied bandwidth; phase noise; I-Q imbalance; clock frequency offset; center frequency leaking; out-of-band noise, adjacent channel couplings or timing, jitter, etc. Such correlating techniques are for example described in more detail in the publication by Q.H. Tran, S. Wane, F. Terki, D. Bajon, A. Bousseksou, J. A. Russer, P. Russer, entitled "Toward Co-Design of Spin-Wave Sensors with RFIC Building Blocks for Emerging Technologies", 2018 2nd URSI Atlantic Radio Science Meeting (AT-RASC), the contents of this publication being hereby incorporated by reference. Furthermore, it is possible to perform wireless measurements of power levels and energy density levels at DC and RF/Microwave frequencies, and entropy extraction, as described for example in more detail in the publication by S. Wane et al. entitled "Energy-Geometry-Entropy Bounds aware Analysis of Stochastic Field-Field Correlations for Emerging Wireless Communication Technologies", URSI General Assembly Commission, New Concepts in Wireless Communications, Montreal 2017), the contents of this publication being hereby incorporated by reference. [0071] Figure 13 schematically illustrates a pair of adjacent sensing modules 400, 400' of the array 1200 of Figure 12, one for X-polarization and one for Y-polarization. Each of the modules 400, 400' is for example biased by a corresponding voltage regulator of its embedded integrated circuit. For example, the terminals of the spin-wave sensor of each of the sensing modules 400, 400' of Figure 13 include pairs A and D for applying the DC biasing voltage, and pairs B and C for outputting the detected signal from the spin-wave sensors of the modules 400, 400'.

[0072] Figure 14 is a plan view of a near-field scanning system 1400 configured to displace the probe array 1200 in two dimensions. For example, the system 1400 comprises a platform 1402 on which the probe array 1200 is mounted, a stepper motor 1404 configured to displace the platform in an x direction, and a stepper motor 1404 configured to displace the platform in a y direction. For example, the stepper motors are configured to displace the platform 1042, and thus the probe array 1200, by steps of fixed length in each of the x and y directions, where the fixed length in each direction is less than the pixel pitch in that direction, such that the system 1400 permits a resolution of the probe array 1200 to be increased.

[0073] Figure 15 schematically illustrates a system 1500 comprising the probe array 1200 and a control board 1504. The probe array 1200 for example comprises 64 sensing modules 400, 400' arranged in lines and rows. In the example of Figure 15, the array 1200 is formed on a support substrate having tongues 1506 along at least one side and adapted to engage with corresponding grooves a further support substrate (not illustrated) that can be added to extend the side of the array [0074] The probe array 1200 is coupled to the control board 1504 via a wired communications interface 1508, although in alternative embodiments a wireless interface could be implemented. The interface 1508 for example permits high data rate serial communication between the array 1200 and the board 1504.

[0075] The control board 1504 for example comprises at least two analog to digital converters (ADC), and in the example of Figure 15, there are 16 ADCs labelled ADC1 to ADC16. The ADCs are for example configured to convert one or more signals detected by the sensing modules of the array. For example, switches are used to sequentially select lines or rows of elements of the array to be sampled, and the 16 ADCs permit an entire row, or an entire line, of sensing modules to be read at the same time.

[0076] The control board 1504 also for example comprises mixers (MX) for down-converting signals received via the sensors of the array, for example prior to analog to digital conversion. This is for example performed when the frequency of the received signals are in the millimeter wave range of 24.24 GHz or above, or even for relatively high RF frequencies of 5 GHz or above. In some embodiments, there is a mixer for every ADC. Furthermore, in some embodiments, other functions such as amplification by one or more LNAs (Low Noise Amplifier), filtering by one or more filters, etc., may also be performed.

[0077] The control board 1504 also for example comprises a processing device, which is for example a field-programmable gate array (FPGA), a memory (MEM), which is for example an SRAM (static random access memory) or a non-volatile memory such as a FLASH memory. The control board 1504 also comprises, in some embodiments, one or more digital to analog converters (DAC) configured to generate the DC supply voltage supplied to each of the sensing modules.

[0078] Figure 16 schematically illustrates a sensing device 1600 comprising a plurality of pixels, there being four pixels Pixel-1 to Pixel-4 in the example of Figure 16. Each pixel comprises a pair of sensing modules 400, 400'. The sensing modules 400 are for example coupled to an X-polarization tuning circuit (CTRL X-POL) 1602, which for example provides a DC-control signal for simultaneous or sequential selection of field components to be measured. Similarly, the sensing modules 400' are for example coupled to a Y-polarization tuning circuit (CTRL Y-POL) 1604, which for example also provides a DC-control signal for simultaneous or sequential selection of field components to be measured.

[0079] Outputs of the sensing modules 400 are for example provided to a four-channel processing circuit (4 CHANNEL RFIC: X-POL) 1606, which provides an x polarization output signal XOutput . Similarly, outputs of the sensing modules 400' are for example provided to a four-channel processing circuit (4 CHANNEL RFIC: Y-POL) 1608, which provides an x polarization output signal XOutput.

[0080] Figure 17 schematically illustrates a readout circuit 1700 for a probe array, in which two channels (CHANNEL A, CHANNEL B) of probing elements are present in a sensor layer (SENSOR LAYER) 1706, each channel comprising N probing circuits (Pixel-lxy to Pixel-Nxy). For example, the presence of two channels permits addition information to be gathered. A multiplexing layer (MULTIPLEXING LAYER) 1702 for example comprises multiplexers configured to combine the antenna outputs on a reduced number of lines. For example, in one embodiment, for each channel A, B there is one multiplexer (MUX X-POL) for combining the X-polarization signals to a single line, and another multiplexer (MUX Y-POL) for combining the Y-polarization signals to a single line. Each multiplexer for example receives, on separate lines, the outputs from the RF/millimeter wave sensors and the outputs from the spin-wave sensors. The channel A multiplexers are for example controlled by a control signal C-A generated by a control circuit (not illustrated in Figure 17) and the channel B multiplexers are for example controlled by a control signal C-B generated by the same control circuit or another control circuit.

[0081] The output lines of the multiplexers are for example provided to radio frequency integrated circuits (RFIC) 1712 for channel A, and 1714 for channel B. The RFICs 1712, 1714 for example form part of a signal conditioning layer (SIGNAL COND. LAYER) of a control board 1704, which is for example similar to the board 704 of Figure 7. The signal conditioning layer may additionally comprise further functions, such as down-conversion, low noise amplification, filtering, etc. The output signals from the RFIC 1712 provide the measurement signal of channel A (MES. SIGNAL CHANNEL A) and the measurement signal of channel B (MES. SIGNAL CHANNEL B), these signals then being processed by an ADC layer (ADC LAYER) 1710.

[0082] While not illustrated in Figure 17, a similar arrangement of multiplexers is for example used in the inverse direction for supplying biasing voltages, for example DC voltages, to the probing elements, these voltages for example being generated by one or more DACs.

[0083] The measured channel A and channel B signals are for example outputted to corresponding mixers 1718, 1720, each operating based on a same reference frequency supplied, for example, by a local oscillator 1722, in order to provide up or down-conversion. The outputs of the mixers 1718, 1720 are for example supplied to a signal processing and analysis circuit 1724.

[0084] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art.

[0085] Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.

Claims

1.A sensing device for sensing magnetic and/or electro magnetic fields comprising a first sensing module comprising:

- a first tier comprising an integrated circuit chip implementing at least an amplifier; and

- a second tier positioned over the first tier, the second tier comprising a spin-wave sensor having at least first and second connection nodes, wherein the first connection node of the spin-wave sensor is coupled to a first input of the amplifier.

2. The sensing device of claim 1, wherein the amplifier is a differential amplifier, and a second connection node of the spin-wave sensor is coupled to a second input of the amp1ifier.

3. The sensing device of claim 2, wherein the spin-wave sensor further comprises third and fourth connections nodes, and the integrated circuit chip further comprises a regulator configured to apply a voltage or current across the third and fourth connection nodes.

4. The sensing device of any of claims 1 to 3, wherein the spin-wave sensor has a multi-layer structure comprising a ferromagnetic layer and an antiferromagnetic layer.

5. The sensing device of claim 4, wherein the multi-layer structure further comprises a non-magnetic layer, for example of copper, between the ferromagnetic and antiferromagnetic layers.

6. The sensing device of any of claims 1 to 5, further comprising a substrate on which the first tier is positioned .

7. The sensing device of any of claims 1 to 6, wherein the spin-wave sensor comprises a plurality of contact pads coupled to the integrated circuit chip via wire bonding and/or via a plurality of micro bumps.

8. The sensing device of any of claims 1 to 7, wherein the first sensing module is in the form of a package comprising a mounting surface for mounting the package to a substrate, wherein the mounting surface comprises a plurality of micro-bumps for providing electrical connections to the substrate.

9. The sensing device of claim 8, further comprising a further substrate on which the first sensing module is mounted.

10. The sensing device of claim 9, wherein the further substrate comprises a shielding layer formed of a metal, and wherein input/output terminals of the first sensing module are coupled to a via passing through an opening in the shielding layer.

11. The sensing device of claim 9 or 10, further comprising a second sensing module mounted on the substrate, wherein the first and second sensing modules are oriented so as to receive signals of opposite polarizations to each other .

12. The sensing device of claim 11, comprising a sensor network formed of a 1-dimensional, 2-dimensional or 3- dimensional array of pixels, each pixel comprising the first and second sensing modules.

13. The sensing device of claim 12, wherein the sensor network is mounted on a near-field scanning system configured to displace the sensor network by steps of fixed length in each of one or more directions, where the fixed length in each direction is less than the pixel pitch in that direction.

14. A test system comprising: the sensing device of claim 12 or 13; and a control board coupled to the sensing device, the control board comprising at least two mixers (MX) configured to down-convert the frequencies of signals received by one or more of the sensing modules into digital signals; and at least two analog to digital converters (ADC1-ADC16) configured to convert the down-converted signals into digital signals.