An electron spin resonance spectroscopy system

Abstract

Described herein is an electron spin resonance (ESR) microsystem, including: one or more microcoils, a first and second amplifier, and a mixer, wherein the one or more microcoils, the first and second amplifiers, and the mixer are located on a single chip, and wherein the microsystem is suitable for performing pulsed ESR spectroscopy on a test sample positioned at or near the one or more microcoils by being configured to perform the steps of: producing a magnetic field in the one or more microcoils, generating one or more ESR signals in the one or more microcoils based on a response of the test sample to the magnetic field produced by the one or more microcoils, amplifying, using the first amplifier, the one or more ESR signals generated by the one or more microcoils, down-converting, using the mixer, the one or more amplified ESR signals amplified by the first amplifier, and amplifying, using the second amplifier, the one or more down-converted ESR signals down-converted by the mixer.

Description

AN ELECTRON SPIN RESONANCE SPECTROSCOPY SYSTEM TECHNICAL FIELD

[0001] The embodiments described herein broadly relate to an electron spin resonance (ESR) spectroscopy system. BACKGROUND

[0002] Electron spin resonance (ESR) spectroscopy finds a wide range of applications in various scientific disciplines, including chemistry, physics, biology, and materials science. It is especially valuable in the study of free radicals, transition metal ions, and defects in crystals, providing crucial information about their electronic and geometric structures. Since the first successful ESR signal observation by Zavoisky in 1944, the instrumentation for ESR spectroscopy has covered an increasingly broader range of operating frequencies and magnetic fields, sample volumes, temperatures, pressures, and excitation / detection methods.

[0003] A promising approach for high sensitivity and low cost ESR spectroscopy on nanoliter and subnanoliter samples is the integration of the sensitivity relevant part of the spectrometer into a single chip having an area of less than 1 mm2. Several single chip integrated ESR microsystems have been reported in the last 15 years, with operating frequencies from 8 to 260 GHz and operating temperatures from 1.4 to 300 K. Previously reported single chip integrated ESR microsystem are based on continuous wave (CW), rapid scan, and pulsed excitations. The reported sensitivity of these sensors are in range from 107to 1012spins / Hz1 / 2depending on the operating frequency, temperature, and sensitive volume.

[0004] Methods based on pulsed excitation have been first implemented for nuclear magnetic resonance (NMR) spectroscopy, where they proved to be far superior to CW excitation methods in terms of richness of information that can be extracted. Today, all commercial NMR systems for spectroscopy and imaging are based on pulsed excitations. The pulsed excitation is very commonly used also for ESR spectroscopy, although CW techniques are still used in many industrial and research applications. Pulsed techniques combined with miniaturized conducting and superconducting resonators have been used for ESR spectroscopy of nanoliter and subnanoliter samples.SUMMARY

[0005] It is desirable to provide an electron spin resonance (ESR) spectroscopy system, for example a single chip integrated pulsed ESR microsystem. Additionally or alternatively, it is desirable to provide the industry with a useful choice.

[0006] In one aspect, there is provided an electron spin resonance (ESR) microsystem, including: one or more microcoils, a first and second amplifier, and a mixer, wherein the one or more microcoils, the first and second amplifiers, and the mixer are located on a single chip, and wherein the microsystem is suitable for performing pulsed ESR spectroscopy on a test sample positioned at or near the one or more microcoils by being configured to perform the steps of: producing a magnetic field in the one or more microcoils, generating one or more ESR signals in the one or more microcoils based on a response of the test sample to the magnetic field produced by the one or more microcoils, amplifying, using the first amplifier, the one or more ESR signals generated by the one or more microcoils, down- converting, using the mixer, the one or more amplified ESR signals amplified by the first amplifier, and amplifying, using the second amplifier, the one or more down-converted ESR signals down-converted by the mixer.

[0007] In some embodiments, the microsystem is a single chip integrated ESR microsystem or part thereof.

[0008] In some embodiments, the one or more coils is coupled to the first amplifier.

[0009] In some embodiments, the first amplifier is coupled to the one or more coils, and the mixer.

[0010] In some embodiments, the first amplifier is located between the one or more coils and the mixer.

[0011] In some embodiments, the mixer is coupled to the first amplifier and the second amplifier.

[0012] In some embodiments, the mixer is located between the first amplifier and the second amplifier.

[0013] In some embodiments, the second amplifier is coupled to the mixer.

[0014] In some embodiments, the first amplifier is a low noise amplifier (LNA), optionally an X-band LNA.

[0015] In some embodiments, the mixer is a double balanced mixer (DB-mixer).

[0016] In some embodiments, the second amplifier is a low frequency (LF) amplifier or an intermediate frequency (IF) amplifier.

[0017] In some embodiments, the IF amplifier has an operating bandwidth from around DC to around 350 MHz.

[0018] In some embodiments, the microsystem is configured to operate within or around an X-band frequency range, for example from 8.8 to 9.8 GHz.

[0019] In some embodiments, the microsystem has a power rating of around 100 mW or less.

[0020] In some embodiments, the microsystem includes one or more filters.

[0021] In some embodiments, the microsystem is configured to operate with a measured spin sensitivity of about 7x107spins / Hz1 / 2on a (sensitive) volume of about 0.1 nL (or less).

[0022] In some embodiments, the chip and / or microsystem is around 1mm2 or less in area, and optionally around 0.7 mm2 in area.

[0023] In some embodiments, the one or more microcoils includes an excitation microcoil and a detection microcoil.

[0024] In some embodiments, the detection microcoil, first amplifier, mixer, and second amplifier are electrically coupled together as an integrated ESR receiver circuit.

[0025] In some embodiments, the excitation microcoil is co-integrated with the integrated ESR receiver circuit.

[0026] In some embodiments, the excitation microcoil and detection microcoil are located on the same plane.

[0027] In some embodiments, the exciation microcoil and detection microcoil are concentric.

[0028] In some embodiments, the detection microcoil is smaller in diameter than the excitation microcoil.

[0029] In some embodiments, the ESR microsystem is further configured to perform one or more of the following steps of: receiving the test sample at or near a first microcoil and / or a second microcoil, producing a magnetic field in the first microcoil, and inducing a current in the second microcoil based on the produced magnetic field of the first microcoil.

[0030] In another aspect, there is provided a method of performing electron spin resonance (ESR) spectroscopy with an ESR microsystem according to any embodiment of the previous aspect.

[0031] In another aspect, there is provided a method of performing electron spin resonance (ESR) spectroscopy with an electron spin resonance (ESR) microsystem comprising the steps of: placing a test sample at or near a detection microcoil, producing a microwave magnetic field in an excitation microcoil, inducing a microwave current in the detection microcoil based on the produced microwave magnetic field of the excitation microcoil, producing a microwave magnetic field in the detection microcoil based on the induced microwave current in the detection microcoil, generating one or more ESR signals in the detection microcoil based on a response of the test sample to the magnetic field produced by the detection microcoil, amplifying, using a low noise amplifier (LNA), the one or more ESR signals generated by the detection microcoil, down-converting, using a double- balanced mixer (DB-mixer), the one or more amplified ESR signals amplified by the LNA, and amplifying, using an intermediate frequency (IF) amplifier or low frequency (LF) amplifier, the one or more down-converted ESR signals down-converted by the DB-mixer.

[0032] In some embodiments, the ESR microsystem includes the detection microcoil, excitation microcoil, LNA, DB-mixer, and the IF amplifier or LF amplifier.

[0033] In some embodiments, the detection microcoil, excitation microcoil, LNA, DB- mixer, and the IF amplifier or LF amplifier are located on a single chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figs.1(a)-(e) show a first exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0035] Figs. 2 shows a set up for experimenting with the first exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0036] Figs. 3(a)-(c) show experimentation results performed with the first exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0037] Figs. 4(a)-(f) show experimentation results performed with the first exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0038] Figs. 5(a)-(c) show a second exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0039] Fig.6 shows a set up for experimenting with the second exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0040] Fig. 7 show experimentation results performed with the second exemplary embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0041] Fig. 8 shows a general embodiment of the pulsed ESR spectroscopy microsystem or circuit.

[0042] Fig. 9 shows a flow diagram of an exemplary method embodiment of performing ESR spectroscopy with any ESR microsystem embodiment disclosed herein. DETAILED DESCRIPTION 1. Overview

[0043] By way of background, a pulsed Electron Spin Resonance (ESR) microsystem is a tiny, integrated device designed to detect and analyse the behaviour of unpaired electrons in materials at a very small scale.

[0044] The detailed description provided herein broadly relate to embodiments of a pulsed ESR microsystem / circuit. The embodiments of the pulsed ESR microsystem described herein may be used in the field of quantum technology, including for materials science, quantum sensing and quantum computing, as it would offer researchers, scientists, engineers and technologists a tool for studying and harnessing the behaviour of unpaired electrons in materials. 1.1 General embodiment

[0045] Description turns to a general embodiment of the ESR microsystem / circuit with respect to Fig.8.

[0046] Fig. 8 is a block diagram showing a general embodiment of a ESR microsystem / circuit 1. In the example of Fig.8, the ESR microsystem / circuit 1 is integrated into (or part of) a single chip 2, i.e. an integrated circuit. In turn the single chip 2 is located on a printed circuit board (PCB) 3. The ESR microsystem / circuit 1 is used as part of an experimental set up 4 for conducting pulsed ESR spectroscopy experiments. Experimental set up 4 may be referred to as an ESR spectrometer 4 herein.

[0047] Referring to the components of the ESR microsystem / circuit 1. The ESR microsystem / circuit 1 includes one or more microcoils 10. The ESR microsystem / circuit 1 includes a first amplifier 20. The ESR microsystem / circuit 1 includes a mixer 30. The ESR microsystem / circuit 1 includes a second amplifier 40. Such configuration makes the ESR microsystem / circuit 1 suitable for performing pulsed ESR spectroscopy experiments.

[0048] Referring to the arrangement shown in Fig. 8, the first amplifier 20 is coupled to the one or more coils 10, and the mixer 30. More particularly, the first amplifier 20 is located between the one or more coils 10 and the mixer 30. The mixer 30 is coupled to the first amplifier 20 and the second amplifier 40. More particularly, the mixer 30 is located between the first amplifier 20 and the second amplifier 40. The second amplifier 40 is coupled to the mixer 30.

[0049] Any component making up the ESR microsystem / circuit 1 (that is, the one or more microcoils 10, first amplifier 20, mixer 30, and second amplifier 40) may be considered sub- circuit, a portion, or a region of the ESR microsystem / circuit 1.

[0050] The ESR microsystem / circuit 1 is suitable for performing pulsed ESR spectroscopy on a test sample positioned at or near the one or more microcoils 10 as follows. The ESR microsystem / circuit 1 is configured to produce a magnetic field in the one or more coils. The ESR microsystem / circuit 1 is also configured to generate one or more ESR signals in the one or more microcoils 10 based on a response of the test sample to the magnetic field produced by the one or more microcoils 10. The ESR microsystem / circuit 1 is also configured to amplify, using the first amplifier 20, the one or more ESR signals generated by the one or more microcoils 10. The ESR microsystem / circuit 1 is also configured to down-convert, using the mixer 30, the one or more amplified ESR signals amplified by the first amplifier 20. The ESR microsystem / circuit 1 is also configured to amplify, using the second amplifier 40, the one or more down-converted ESR signals down-converted by themixer 30. For reference, the arrows pointing right in Fig.8 indicate the direction of the one or more ESR signals through the ESR microsystem / circuit 1.

[0051] In the example of Fig.8, there are two microcoils: an excitation microcoil 10a, and a detection microcoil 10b. Although the example of Figure 8 shows two microcoils, this is merely an example only, and it is possible using a single microcoil instead to act as both the excitation microcoil and detection microcoil. That is, for some embodiments, only a single microcoil is used for excitation and detection. In some embodiments, the microcoil(s) used for excitation and / or detection may be incorporated as part of the first amplifier 20 (see Fig. 1(e) for example). In some embodiments, the excitation microcoil 10a and the detection microcoil 10b are located on the same plane. In some embodiments, the excitation microcoil 10a and the detection microcoil 10b are concentric, of which one example may include the detection microcoil 10b being smaller in diameter than the excitation microcoil 10a.

[0052] In some embodiments, the first amplifier 20 is a low noise amplifier (LNA), optionally an X-band low noise amplifier. In some embodiments, the mixer 30 is a double- balanced mixer (DB-mixer). In some embodiments, the second amplifier 40 is an intermediate frequency (IF) amplifier. Alternatively, the second amplifier is a low frequency (LF) amplifier.

[0053] In some embodiments, the excitation microcoil 10a, detection microcoil 10b, LNA 20, DB-mixer 30, and IF amplifier 40 are located or integrated on the same chip 2. In some embodiments, the detection microcoil 10b, LNA 20, DB-mixer 30, and IF amplifier 40 are electrically coupled together as an integrated ESR receiver circuit, such as Fig. 1(e) for example. In such embodiment, the ESR microsystem / circuit may comprise of an integrated receiver circuit, and a co-integrated excitation microcoil.

[0054] Two exemplary embodiments falling within the scope of the pulsed ESR microsystem / circuit general embodiment 1 will later be described in turn with respect to Figs.1-7: • Section 2 describes a first exemplary embodiment 101 with respect to Figs.1-4. The first exemplary embodiment 101 includes: an excitation microcoil 110a, a detection microcoil 110b, a low noise amplifier 120, a double-balanced mixer 130, and an intermediate frequency amplifier 140. The first exemplary embodiment 101 is integrated as part of a chip 102, which in turn is located on a PCB 103. The exemplaryembodiment 101 is used with a set up 104 to obtain pulsed ESR spectroscopy experimentation results. • Section 3 describes a second exemplary embodiment 201 with respect to Figs.5-7. The second exemplary embodiment 201 includes: an excitation microcoil 210a, a detection microcoil 210b, a low noise amplifier 220, a double-balanced mixer 230, and a low frequency amplifier 240. The first exemplary embodiment 201 is integrated as part of a chip 202. The exemplary embodiment 201 is used with a set up 204 to obtain pulsed ESR spectroscopy experimentation results.

[0055] As will be apparent from the remainder of the detailed description, the general embodiment of the pulsed ESR microsystem / circuit 1 (and / or exemplary embodiment(s) thereof ) may provide one or more of the following effects: • One or more described embodiments of the pulsed ESR microsystem / circuit are configured for pulsed ESR experiments with a good sensitivity and signal-to-noise ratio. The good sensitivity and signal-to-noise ratio may be achieved with the selection of a relatively small detection coil and a relatively low noise amplifier (LNA). Experimental results provided herein show that is it possible to achieve an improved sensitivity while the ESR microsystem and spectrometer operate at room temperature and in the X-band range (e.g. at or around 9 GHz). The experimental spin sensitivity that can be achieved experimentally by the disclosed ESR microsystem embodiment is 7 × 107spins / Hz1 / 2on a sensitive volume of approximately 0.1 nL. However, as will be apparent in the experiments described later, the sensitive volumes used in the experiments are varied and may be less than 0.1 nL: o The volume of 0.1 nL corresponds to dimensions of 60 µm x 60 µm x 30 µm, which is a half cube with a 60 µm side. The 60 µm side is shorter than the external turn side of the detection microcoil (e.g.80 µm), and longer than the internal turn side of the microcoil (e.g. 50 µm). The sample volumes in the experiments described herein may be smaller than a sample dimensioned 60 µm x 60 µm x 30 µm, however a sample of 60 µm x 60 µm x 30 µm placed on top of the detection microcoil the spin sensitivity would be very similar to the experimentally measured spin sensitivity of 7 × 107spins / Hz1 / 2experimentally obtained with test samples having smaller volume than 0.1 nL. • One or more described embodiments of the pulsed ESR microsystem / circuit facilitate a miniaturisation and simplification of the pulsed ESR system. That is, one or more embodiments of the pulsed ESR microsystem described herein include components integrated onto or within a single chip, resulting in a compact and portable design. For example, one or more embodiments of the pulsed ESR system is small enough to occupy a footprint of around 0.7 mm2. This miniaturisation not only reduces the footprint of the system but also simplifies setup and operation, making it more convenient for use and enabling potential applications in on-chip sensing and spectroscopy. This stands in contrast to traditional ESR systems that often entail bulky and complex setups with components, plant, and equipment that require significant space and resources. • One or more described embodiments of the pulsed ESR microsystem / circuit may provide ease of use and automation, fast response times, and potential for on-chip signal processing. 2. First Exemplary embodiment

[0056] Description turns to a first exemplary embodiment 101 with respect to Figs.1-4. 2.1 Implementation

[0057] Description of a first exemplary embodiment of the ESR microsystem will now be provided with respect to Figs.1(a)-(e). In particular, Figure 1 shows a single chip integrated pulsed ESR microsystem with the following features: • Fig.1(a) shows a printed circuit board (PCB) with the single chip integrated pulsed ESR microsystem. The chip is glued on the PCB and electrically connected by Au wire bonding. • Fig. 1(b) shows a photograph of the pulsed ESR microsystem. The red rectangle indicates the excitation and detection microcoils. Fig.1(b) is a close up view of the pulsed ESR microsystem seen in Fig.1(a).• Fig.1(c) shows a block diagram of the single chip pulsed ESR microsystem. VDDRXis connected to several nets and the connections are not shown in the schematic for simplicity. VDDRX is the supply voltage of all the blocks in the microsystem. • Fig. 1(d) shows a photograph of the excitation and detection microcoils. The excitation microcoil has one turn. The receiver microcoil has two turns. Fig.1(d) is a close up view of the excitation and detection microcoils seen in Fig.1(b). • Fig.1(e) shows a transistor level schematic of single chip pulsed ESR microsystem seen in Fig.1(c). The connections in red color are the input and output pads of the microsystem (i.e. VDD, VLOP, VLON, OUTP, OUTN, and GND). The green connections are internal connections and connections to the biasing circuits (i.e. RFP, RFN, VIFP, VIFN, Vbias, Vbias2, Vb, and Vb1).

[0058] The single chip integrated pulsed ESR microsystem includes a complete receiver operating at X-band and a co-integrated excitation microcoil. The chip is manufactured in a 130 nm SiGe BiCMOS technology (IHP SG13G2Cu). The chip, shown in Fig.1(b), has an area of 0.7 mm2including the bonding pads and operates with a supply voltage VDDRX in the range from 1 to 2.5 V and a corresponding current from 20 to 40 mA. Hence, the chip power consumption is in the range from 20 to 100 mW.

[0059] The excitation microcoil is a one turn coil with an outer diameter of 180 µm and a width of 10 µm implemented with a 2.8 µm thick Al layer. The excitation microcoil is centered around the detection microcoil as shown in Fig.1(d). Its inductance is 500 pH and its series resistance is 1.8 Ω. The excitation microcoil is bonded to a standard FR4 (1.6 mm thickness) PCB, using two 1.8 mm length 20 µm Au wires. One side of the microcoil is grounded on the PCB and the other one is connected to a 50 Ω transmission line. No tuning / matching circuitry is used in the excitation path. The excitation frequency is set at the frequency with minimum power reflection.

[0060] The single chip pulsed ESR receiver includes a detection microcoil, an X-band low noise amplifier (LNA), a double-balanced mixer (DB-mixer), and an intermediate frequency (IF) amplifier. The receiver has maximum simulated total single output gain of 64 dB (V DDRX = 1.8V) and 76 dB (V DDRX = 2.5 V), i.e., the differential gain is 70 dB and 82 dB, respectively. The receiver chain block diagram is shown in Fig. 1(c) and its detailed schematics are shown in Fig.1(e). The detection microcoil is a two turns planar rectangularinductor implemented using a 3.2 µm thick Cu layer. It has an outer diameter of 80 µm, a wire width of 10 µm, and spacing between wires of 5 µm. The detection microcoil has an inductance of 300 pH and a resistance of 1.5 Ω. The LNA has a 3 dB bandwidth of 2 GHz about 9.5 GHz (i.e., 8.5 to 10.5 GHz) and a maximum gain of 23 dB. The detection coil is resonated with a parallel 1 pF capacitance and amplifies the induced signal and noise by a factor of 10. The resulting gain at the output of the LNA including the microcoil resonance gain is 43 dB. This resonance determines an effective 3 dB bandwidth from 9.2 to 10 GHz for the ESR signal induced in the detection microcoil. The input referred simulated voltage noise is about 0.3 nV / Hz1 / 2, which includes the thermal noise of the detection microcoil and the equivalent input noise of the receiver electronics. The excitation and detection microcoils are concentric and located in the same plane. Hence the microwave magnetic field produced by the excitation coil results in an induced microwave electromotive force and hence a microwave current in the detection microcoil. The detection microcoil is connected to the LNA, which has an input impedance (i.e., between pins A and B shown in Fig.1(e)) of about (400 Ω || 200 fF). By considering the LNA input impedance and the detection resonator impedance, the microwave current induced in the detection microcoil produces a microwave magnetic field ^^1which is approximately four times larger than the one produced by the current running into the excitation microcoil. Measurements and simulations indicate that the maximum microwave magnetic field B1at the center of the detection microcoil is about 8 G with an input power of 10 W.

[0061] The amplified signal by the LNA is frequency down converted through a double balanced mixer (DB-mixer) with an input bandwidth from 7 to 12 GHz. The DB-mixer has a maximum gain of 8 dB and an output bandwidth from DC to 500 MHz. In this design, the mixer LO signal are fed externally in the form of two sinusoidal signals with π phase difference. Both LO inputs are DC biased at a voltage that can vary from 1 to 1.8 V. The next stage is a differential IF amplifier having a bandwidth from DC to 350 MHz and maximum gain of 14 dB. The output stage of the IF amplifier is capable to drive external electronics with 50 Ω input impedance.

[0062] As can be seen in Fig.1(e), filters are used throughout the ESR microsystem. The detection coil has a parallel capacitor, the (medium wave (MW)) LNA amplifier has acapacitor and inductors inside for filtering, and the IF amplifier has capacitors to configure the bandwidth.

[0063] The expected spin sensitivity can be computed as follow. The initial amplitude of the electromotive force induced in the detection coil by the spin precession after a π / 2 flip angle, is: ^^0 = ^^0^^^^^^^^0^^^^ (1)

[0064] where ^^0 = γ^^0 is the Larmor frequency (in rad / s), ^^0 is the static magneticfield (in T), γ is the gyromagnetic ratio (in rad / sT), ^^^^^^is the component of the unitary magnetic field of the detection coil perpendicular to ^^0(in T / A), ^^0is the static magnetisation (in A / m), and ^^^^is the sample volume (in m3). The static magnetisation inthe Curie law approximation ^^^^ ≫ is0 3^^^^^^ (2)

[0065] where N is the number of spins per unit volume (in spins / m3), ℏ is the reduced Planck constant, S is the spin quantum number, T is the sample temperature (in K), and kBis the Boltzmann constant. The spin sensitivity (in spins / Hz1 / 2) can be defined as ^^^^^^^^= ^^^^ / ^^^^^^, where ^^^^is the number of spins in the sample, ^^^^^^ is the signal to noise ratio (in1 / Hz1 / 2) defined as ^^^^^^ = ^^0 / ^^^^, and ^^^^ is voltage noise spectral density at the coil ends(in V / Hz1 / 2). Hence the spin^^^^^^^^1^^γ3ℏ2^^(^^+1)^^20(3)

[0066] In the following we compute the expected spin sensitivity for the ESR receiver described above. For a planar coil that includes two close-by turns, the unitary magnetic field in the centerthe coil is ^^^^^^≅2µ0 / ^^, where d is the diameter of the detection microcoil. Hence, for ^^≅ 65 µm, we have ^^^^^^≅ 0.04 T / A. As discussed above, the voltage noise spectral density at the coil ends is Vn ≅ 0.3 nV / Hz1 / 2. From these values and assuming S = 1 / 2, B0≅ 0.3 T, γ ≅ 2π × 28.04 GHz / T, T = 293 K, the expected spin sensitivity is Nmin≅ 2 × 107spins / Hz1 / 2. 2.2. Experimental set-up and results

[0067] Description of the experimental set-up and results with respect to the first exemplary embodiment of the ESR microsystem will now be provided with respect to Fig. 2, and Figs.3(a)-(c).

[0068] The experiments conducted on the first exemplary embodiment of the ESR microsystem are performed at room temperature, in air, and in an ordinary laboratory without RF / MW shielding. The chip is glued on top of an FR4 printed circuit board (PCB) as shown in Fig. 1(a) using conductive epoxy (Epo-Tek, H20E-FC). The electrical connections from the chip to the PCB are made by wedge-wedge Au bonding wires having a diameter of 20 µm. The PCB is placed in a 0 to 2 T resistive electromagnet. The connection from the PCB to the external electronics are realized with four coaxial cables for the RF / MW connections (LOP, LON, EXC, VOUT P) and three single pole wires for the DC connections (VDDRX, GND, VLO).

[0069] Fig. 2 shows the set up used to conduct the experiments on the first exemplary embodiment of the single chip pulsed ESR microsystem. The red lines are the MW connections, the black lines are the GPIB connections and DC power lines, the blue lines are the LVTTL pulses, and the green lines are the IF signals. Fig. 2 also shows a number of features in the experimental set up as follows: • (A) Room temperature bore resistive electromagnet (0 to 2.1 T, Bruker). • (B) Vacuum chamber connected to a turbomolecular pump (for the experiments in this work we worked in air). • (C) Frequency synthesizer (Valon 5019). • (D) 10 to 15 dB attenuator. • (E) Power splitter (Mini-Circuits, ZX10-2-126). • (F) Phase adjuster (Spectrum, LS-0012-2121). • (G) High speed programmable pulse generator (SpinCore, PBESR-PRO-500-USB- RM-FP). • (H) LVTTL SPDT non-reflective switch (Analog Devices, ADRF5024). • (I) USB Oscilloscope (Keysight, P9242A). • (J) 3 dB attenuator. • (K) Power amplifier (MITEQ, AMF-6B-09501050-40P). • (L) Power supplies.• (M) Magnet power supply (0 to 150 A, Bruker). • (N) Signal generator (Rohde & Schwarz SMR 20). • (O) Switch (Mini-Circuits ZYSW-2-50DR). • (P) Frequency mixer (Mini-Circuits ZX05-153-S+). • (Q) SPDT non-reflective switch (Mini-Circuits ZYSW-2-50DR). • (R) Low noise amplifier (Mini-circuits, ZFL1000-LN+). • (S) SPDT non-reflective switch (Analog devices ADRF5142). • (T) Frequency divider with TTL output (Valon 3010).

[0070] As shown in Fig. 2, two microwave signal generators are used for the excitation and LO signals. The LO signal is splitted into two signals (LOP and LON), one of them is π phase shifted before reaching the chip. LOP and LON signals are separately biased using two 1 kΩ resistors soldered on PCB as shown in Fig. 1(a). On the excitation path, three switches (H) are implemented to shape the sinusoidal continuous wave output of the signal generator (N). These switches are controlled by a multichannel programmable pulse generator (G) which produces LVTTL (0-3.3 V) pulses having a minimum length of 6 ns. The use of three switches in series allows to obtain an isolation about 100 dB. A power switch (S) is used after the amplifier to further increase the isolation and to reduce amplifier noise delivered to the excitation coil during the detection time of the ESR signal. In the IF signal path, the switch (Q) prevents the saturation of the external IF amplifier (R), avoiding a significant increase of the deadtime. The two microwave generators are frequency locked using the same 10 MHz reference signal. This assure a fixed frequency difference between the two generators (in our experiments 200 MHz). To allow for phase coherent time domain averaging of the ESR signals, the acquisition is triggered by the IF signal obtained by mixing the two generators using the mixer (P). This IF signal is shaped using the TTL output of a divider (T) and it passes through a switch (O) before reaching the trigger input of the data acquisition board (I). This allows to set the start of the data acquisition at the desired time with respect to the pulse sequence.

[0071] In order to characterize the MW and IF bandwidth of the receiver, we applied a CW signal to the excitation microcoil. The 3 dB microwave bandwidth of the receiver is from 8.8 to 9.8 GHz. The 3 dB IF bandwidth of the receiver is DC to 350 MHz. The measured power consumption is less than 40 mA for a VDDRFof 2.5 V. The maximum AC swing atthe outputs pins VOUT Pand VOUT Nis 400 mV peak-to-peak about a DC level of 1 V. The output noise of the receiver is 250 nV / Hz1 / 2from 1 to 300 MHz. All these experimental results are in agreement with the simulated values reported above.

[0072] In order to exemplify the versatility of the first exemplary embodiment of the ESR microsystem, we performed several conventional pulsed ESR experiments such as single pulse, Rabi nutation, Hahn echo, two echoes, Carr-Purcell (CP) echoes, and inversion recovery echo experiments. For these measurements we used two different samples. A crystal of α, γ-bisdiphenylene- β-phenylallyl (BDPA / benzene, 152560, Sigma-Aldrich) and a sample of 1% BDPA in polystyrene (BDPA:PS). The 1% BDPA:PS sample is prepared using 1 g of polystyrene (PS, 331651, Sigma-Aldrich) solid polymer doped with 10 mg of BDPA (i.e., 1% in weight) using 40 mL of Chloroform (CHCl3) as solvent. The BDPA sample has a spin density of about 1.5 × 1027spins / m3and relaxation times T1≅ T2≅ 100 ns. The 1% BDPA:PS sample has a spin density of about 1.3 × 1025spins / m3and relaxation times T1≅25 µs and T2≅1.1 µs as determined by the experiments shown below. The spin density in 1% BDPA:PS is computed considering that PS has a density of about 1 g / cm3.

[0073] To reduce the off-resonance effects, all experiments are performed with an excitation frequency equal to the Larmor frequency, specifically of about 9.1 GHz in the applied static magnetic field of about 320 mT. As mentioned above, the LO frequency is 200 MHz above the excitation frequency. 2.2.1 Experiments with BDPA

[0074] In this section, we describe the experimental results with respect to Fig. 3, which shows pulsed ESR experiments with BDPA crystals. In particular, Figs.3(a)-(c) show the following features: • Fig. 3(a) shows amplitude of the FID signal at the beginning of the decay as a function of the excitation pulse length TP for two BDPA crystals having different volumes, 50 x 25 x 15 µm3and 25 x 15 x10 µm3, respectively. • Fig.3(b) shows time domain free induction decay (FID) signal of the larger BDPA crystal after 10 ns deadtime. • Fig. 3(c) shows Fast Fourier transform (FFT) of the time domain FID signal. The excitation pulse is 12 ns, the repetition time is 12 µs, and the number of averaging is65000 (i.e., the effective measurement time is less than 1 s). The excitation frequency is 9.1 GHz and the static magnetic field is about 320 mT.

[0075] In Fig.3 are reported experiments performed with two crystals of BDPA having a volume of about 50×25×15 µm3and 25×15×10 µm3. The measured deadtime after the excitation pulse is approximately 5 ns, but it can increase up to 25 ns depending on the applied excitation power and pulse length. In these experiments, the external IF amplifier (device (R) in Fig.2) is not used. In Fig.3(a), the normalized amplitude of the FID signal at the beginning of the decay as a function of the excitation pulse length TP with an excitation power of 36 dBm at the output of the power amplifier is reported. From this measurement we obtain a Rabi nutation frequency (Ω / 2π) of 25 MHz. Hence, the microwave magnetic field B1is Ω / |γe| = 9 G where |γe| = 1.76×1011rad / s is the electron gyromagnetic ratio, in agreement with the simulated value of 8 G of the detection microcoil.

[0076] As shown in Fig. 3(b), the decay time of the Rabi nutation curve of a smaller (25×15×10 µm3) sample is significantly longer. As previously mentioned, most of the microwave magnetic field B1is produced by the induced current in the detection coil. As a result, samples having a volume similar or larger than the detection microcoil are exposed to a more non uniform B1, which explains the shorter decay time of the corresponding Rabi nutation curve. The decay time of the smaller sample is mainly caused by the spin relaxation which is not entirely negligible during the excitation time.

[0077] In Fig.3(b),(c), the free induction decay (FID) signal of the larger crystal after 10 ns deadtime and its Fourier transform obtained with a single π / 2 pulse of 12 ns and an excitation power of 38 dBm is reported. All experiments are performed with a repetition time TR = 12 µs (i.e., 100 times longer than T1), and the number of averaging is 65000 (i.e., the effective measurement time is less than 1 s).

[0078] The measured voltage noise spectral density at the output of the chip is about 0.25 µV / Hz1 / 2in the IF frequency range from 1 to 300 MHz. Considering the density of spins in the sample (1.5 × 1027spins / m3), the sample volume (1.9 × 10−14m3), the voltage noise spectral density (0.25 µV / Hz1 / 2), and the signal amplitude at the beginning of the decay (0.1 V), the experimental spin sensitivity of the single chip pulsed ESR microsystem is 7 × 107spins / Hz1 / 2, i.e., slightly worse than the expected value of 2 × 107spins / Hz1 / 2computed above. 2.2.2 Experiments with 1% BDPA:PS

[0079] In this section, we describe the experimental results with respect to Fig.4, which shows pulsed ESR experiments with a 1% BDPA:PS sample. All the measurements are performed on a 50 x 25 x 15 µm31% BDPA:PS sample at room temperature. The excitation frequency is 9.1 GHz and the static magnetic field is about 320 mT. The repetition time is TR= 1200 µs (i.e., about 50 times longer than T1), and the number of averaging is 1.3 M (i.e., the effective measurement time is about 1600 s). The pulse sequence for each measurement is shown as inset. The dashed lines indicate the parameter that is varied during the experiment. TPis the pulse length. TEis the echo time, which is the time between the π / 2 pulse and the center of the echo in the Hahn and CP echoes sequences. TIis the inversion time, which is the time between the π pulse and the π / 2 pulse in the inversion recovery Hahn echo sequence. T is the time between the TP pulse and the π / 2 pulse in the Ruby nutation Hahn echo sequence. In particular, Figs.4(a)-(f) show the following features: • Fig.4(a) Measured spin echo with TE = 400 ns. • Fig. 4(b) Amplitude of the Hahn echo with TE from 400 to 1600 ns. The measured relaxation time with the Hahn echo sequence is T2= 420 ns. • Fig.4(c) Amplitude of the second echo of the two echoes measurement with TE from 250 to 1500 ns. The measured relaxation time with two echoes measurement is T2= 1100 ns. • Fig.4(d) Amplitude of the Nth echo of CP echoes sequence, where N is the number of π pulses applied after π / 2 pulse. TEis set to 440 ns during the whole experiment. The distance between the π pulses are also constant and equal to TE = 440 ns. The measured relaxation time with the CP echoes sequence is T2 = 600 ns. • Fig.4(e) Amplitude of the Hahn echo measured at a time TI+ TEafter the inversion π pulse. TIis varied from 2 to 200 µs and TE= 600 ns is applied for whole experiment. The measured spin-lattice relaxation time with inversion recovery measurement is T1= 25 µs.• Fig. 4(f) Amplitude of Hahn echo measured T = 6 µs + TE= 600 ns after the pulse of length TP, which is varied from 0 to 100 ns. The Rabi frequency measured is around 12 MHz.

[0080] In Fig. 4 are reported the results of Hahn echo, two echoes, CP echoes, inversion recovery echo, and Rabi nutation echo experiments performed on a sample of 1% BPDA:PS having a volume of about 50×50×20 µm3(i.e., slightly larger than the volume of the BDPA sample measured above). In these experiments, the external IF amplifier (device (R) in Fig. 2) is used to amplify the signal above the output discretization limit of the digitizer (I). The use of the external IF amplifier increases the effective dead time for 25 ns to 100 ns.

[0081] All experiments are performed with a repetition time TR = 1200 µs (i.e., about 50 times longer than T1), and the number of averaging is 1.3 M (i.e., the effective measurement time is about 1600 s).

[0082] Fig.4(a) shows the time domain signal obtained with a Hahn echo experiment (π / 2 − TE / 2 − π) with echo time TE= 400 ns. In Fig.4(b) is reported the amplitude of the echo obtained with Hahn echo experiments performed with echo times TEfrom 400 to 1600 ns. In Fig.4(c) is reported the amplitude of the echo obtained with the two echoes sequence (π / 2 − TE / 2 − π − TE − π) with echo times TE from 250 to 1500 ns. In Fig.4(d) is reported the amplitude of the echo obtained with the CP echoes sequence (π / 2 − TE / 2 − π − TE− π − TE− ...) performed with TE = 440 ns. From the Hahn echo, two echoes, and CP echoes experiments T2 values of 0.42 µs, 1.1 µs and 0.6 µs are extracted, respectively.

[0083] In Fig.4(e) are reported the results of inversion recovery echo experiments (π −TI−π / 2 −TE / 2 −π), performed with inversion time TI from 2 to 200 µs and TE = 600 ns. From the exponential fit of the obtained curve, a relaxation time T1 ≅ 25 µs is obtained.

[0084] In Fig. 4(f) are reported the results of a Rabi nutation echo experiment (Tp− T − π / 2 − TE / 2 − π), performed with Tpfrom 0 to 100 ns, T = 6 µs, TE= 600 ns. From these measurements we obtain a Rabi nutation frequency of about 12 MHz with an excitation power of 38 dBm, smaller than to the value obtained with the Rabi nutation single pulse experiment performed with the BDPA sample presumably due the B1in inhomogeneity and the T time which is not much shorter than T1.

[0085] This concludes description of the first exemplary embodiment of the pulsed ESR microsystem. 3. Second Exemplary Embodiment

[0086] Description turns to a second exemplary embodiment 201 with respect to Figs.5- 7. 3.1. Implementation

[0087] Fig. 5 shows a single chip pulsed ESR microsystem according to a second exemplary embodiment. In particular, Fig.5(a)-(c) show the following features: • Fig. 5(a) shows a block diagram of the single chip ESR microsystem including an integrated microwave receiver with detection microcoil and a co-integrated excitation microcoil. VDDRXis the supply voltage of all the blocks in the receiver circuit. • Fig. 5(b) shows a photograph of the single chip pulsed ESR microsystem. The red rectangle indicates the excitation and receiver microcoils. • Fig.5(c) shows a photograph of the excitation and receiver microcoils. The excitation microcoil has one turn. The receiver microcoil has two turns. Fig.5(c) is a close up view of the excitation and receiver microcoils seen in Fig.5(b). 3.2. Experimental set-up and results

[0088] Description of the experimental set-up and results with respect to the first exemplary embodiment of the ESR microsystem will now be provided with respect to Fig. 6, and Figs.7(a)-(b).

[0089] Fig.6 shows the set up used to conduct the experiments on the second exemplary embodiment of the single chip pulsed ESR microsystem. The red lines represent the lines with 9 GHz signals. The black lines show the control signals, DC power supply, and the generated pulses. Fig.6 shows a number of features in the experimental set up as follows: • A) Room temperature 0-2 T electromagnet (Bruker) • B) Vacuum chamber. • C) Frequency synthesizer (Valon 5019). • D) 3 dB attenuator. • E) Power splitter (Mini-Circuits, ZX10-2-126).• F) Phase adjuster (Spectrum, LS-0012-2121). • G) High speed programmable pulse generator (SpinCore, PBESR-PRO-500-USB- RM-FP). • H) SPDT non-reflective switch (Analog Devices, HMC-C011). • I) USB oscilloscope (5 Gs / s, 500 MHz bandwidth, Keysight, P9242A). • J) 20 to 30 dB attenuators. • K) Power amplifier (MITEQ, AMF-6B-09501050-40P). • L) DC power supplies. • M) Magnet power supply (0-150 A, Bruker). • N) Low noise amplifier (Mini-circuits, ZFL1000-LN+). • O) Control signals for single pulse ESR experiments. CH1 defines the excitation pulse length, CH2 is the trigger for signal acquisition.

[0090] We now describe the experimental results of the second exemplary embodiment with respect to Fig.7, which shows the pulsed ESR experiment performed with a crystal of BDPA having a volume of about 60 x 30 x 20 µm3.

[0091] In order to test the functioning of the second exemplary embodiment of the single chip pulsed ESR microsystem described with respect to Figs.5 (a)-(c), we performed single pulse ESR measurements at room temperature with a crystal of α, γ-bisdiphenylene-β - phenylallyl (BDPA, 152560 Sigma-Aldrich) having a volume of about 60 x 30 x 20 µm3. The results of the performed measurement are reported in Figs. 7(a)-(b). In particular, the real and imaginary part of the FTT (at Fig.7(a)) of the time domain signal (at Fig.7(b)). The excitation pulse is 12 ns, the repetition time is 8 µs (i.e., about 100 times longer than T1), and the number of averaging is 650000 (i.e., the effective measurement time is about 5 s). The excitation frequency is 9 GHz and the static magnetic field is about 320 mT. The deadtime after the pulse is about 50 ns.

[0092] This concludes description of the second exemplary embodiment of the pulsed ESR microsystem. 4. Exemplary method

[0093] An exemplary method 300 of performing electron spin resonance (ESR) spectroscopy with an electron spin resonance (ESR) microsystem (according to any of theembodiments disclosed heretofore) will now be described with reference to Fig.9. At step 310, the method 300 includes placing a test sample at or near a detection microcoil 10b, 110b, 210b. At step 320, the method 300 includes producing a microwave magnetic field in an excitation microcoil 10a, 110a, 210a. At step 330, the method 300 includes inducing a microwave current in the detection microcoil 10b, 110b, 210b based on the produced microwave magnetic field of the excitation microcoil 10a, 110a, 210a. At step 340, the method 300 includes producing a microwave magnetic field in the detection microcoil 10b, 110b, 210b based on the induced microwave current in the detection microcoil 10b, 110b, 210b. At step 350, the method 300 includes generating one or more ESR signals in the detection microcoil 10b, 110b, 210b based on a response of the test sample to the magnetic field produced by the detection microcoil 10b, 110b, 210b. At step 360, the method 300 includes amplifying, using a low noise amplifier (LNA) 20, 120, 220, the one or more ESR signals generated by the detection microcoil 10b, 110b, 210b. At step 370, the method 300 includes down-converting, using a double-balanced mixer (DB-mixer) 30, 130, 230, the one or more amplified ESR signals amplified by the LNA 20, 120, 220. At step 380, the method 300 includes amplifying, using an intermediate frequency (IF) amplifier 40, 140 or low frequency (LF) amplifier 40, 240, the one or more down-converted ESR signals down- converted by the DB-mixer 30, 130, 230. 5. Effects

[0094] One or more embodiments of the ESR microsystem described in this specification may provide one or more of the following effects and / or applications: • In quantum computing, the ability to manipulate and measure electron spins is critical for building qubits – the basic units of quantum information. The pulsed ESR microsystem can aid in characterising and controlling electron spins in quantum systems, contributing new approaches to qubit control and measurement for the development of quantum computing platforms. • The miniaturisation and spin sensitivity opens possibilities for on-chip integration with other components, for the development of integrated quantum sensors. • Ability to conduct a wide range of experiments on different materials and under various conditions with control over the excitation and detection timings. This flexibility is desirable for exploring novel quantum phenomena and optimisingdevice performance for specific applications. E.g. the microsystem can be used to perform advanced experiments such as single pulse, Rabi nutation, Hahn echo, and inversion recovery echo, providing the data for understanding and manipulating electron behaviour. • The technical specifications of the pulsed ESR device make it suitable for long-term and continuous sensing operations. • Portable diagnostics for healthcare applications. E.g. detecting and quantifying free radicals and reactive oxygen species in biological samples, which are implicated in various diseases. • Portable analytical devices. E.g. performing real-time analysis of samples in diverse environments, including remote locations, industrial settings, and point-of-care facilities. • Educational tool. E.g. teaching and learning about quantum physics, spectroscopy, and materials science in classrooms, laboratories, and outreach programs. 6. Disclosed features

[0095] The following clauses list a number of disclosed features as follows: 1. An electron spin resonance (ESR) microsystem, including: one or more microcoils, a first and second amplifier, and a mixer, wherein the microsystem is suitable for performing pulsed ESR spectroscopy. 2. An ESR microsystem according to clause 1, wherein the microsystem is a single chip integrated ESR microsystem or part thereof. 3. An ESR microsystem according to clause 1 or 2, wherein the one or more coils is coupled to the first amplifier.4. An ESR microsystem according to any one of the previous clauses, wherein the first amplifier is coupled to the one or more coils, and the mixer. 5. An ESR microsystem to any one of the previous clauses, wherein the first amplifier is located between the one or more coils and the mixer. 6. An ESR microsystem according to any one of the previous clauses, wherein the mixer is coupled to the first amplifier and the second amplifier. 7. An ESR microsystem according to any one of the previous clauses, wherein the mixer is located between the first amplifier and the second amplifier. 8. An ESR microsystem according to any one of the previous clauses, wherein the second amplifier is coupled to the mixer. 9. An ESR microsystem according to any one of the previous clauses, wherein the one or more microcoils includes an excitation microcoil and a detection microcoil. 10. An ESR microsystem according to any one of the previous clauses, wherein the first amplifier is a low noise amplifier (LNA). 11. An ESR microsystem according to any one of the previous clauses, wherein the mixer is a double balanced mixer (DB-mixer). 12. An ESR microsystem according to any one of the previous clauses, wherein the second amplifier is a low frequency (LF) amplifier or an intermediate frequency (IF) amplifier. 13. An ESR microsystem according to clause 12, wherein the IF amplifier has an operating bandwidth from around DC to around 350 MHz14. An ESR microsystem according to any one of the previous clauses, wherein the microsystem is configured to operate within or around an X-band frequency range, for example from 8.8 to 9.8 GHz. 15. An ESR microsystem according to any one of the previous clauses, wherein the microsystem has a power rating of around 100 mW or less. 16. An ESR microsystem according to any one of the previous clauses, wherein the microsystem includes one or more filters. 17. An ESR microsystem according to any one of the previous clauses, wherein the microsystem is configured to operate with a measured spin sensitivity of about 7x107spins / Hz1 / 2on a sensitive volume of about 0.1 nL. 18. A circuit for performing pulsed electron spin resonance (ESR) spectroscopy, including: one or more microcoils, a first and second amplifier, and a mixer, wherein the circuit is suitable for performing pulsed ESR spectroscopy. 19. A circuit according to clause 18, wherein the circuit is an integrated circuit or part thereof. 20. A circuit according to clause 18 or 19, wherein the one or more coils is coupled to the first amplifier. 21. A circuit according to any one of clauses 18 to 20, wherein the first amplifier is coupled to the one or more coils, and the mixer. 22. A circuit to any one of clauses 18 to 21, wherein the first amplifier is located between the one or more coils and the mixer.23. A circuit according to any one of clauses 18 to 22, wherein the mixer is coupled to the first amplifier and the second amplifier. 24. A circuit according to any one of clauses 18 to 23, wherein the mixer is located between the first amplifier and the second amplifier. 25. A circuit according to any one of clauses 18 to 24, wherein the second amplifier is coupled to the mixer. 26. A circuit according to any one of clauses 18 to 25, wherein the one or more microcoils includes an excitation microcoil and a detection microcoil. 27. A circuit according to any one of clauses 18 to 26, wherein the first amplifier is a low noise amplifier (LNA). 28. A circuit according to any one of clauses 18 to 27, wherein the mixer is a double balanced mixer (DB-mixer). 29. A circuit according to any one of clauses 18 to 28, wherein the second amplifier is a low frequency (LF) amplifier or an intermediate frequency (IF) amplifier. 30. A circuit according to clause 29, wherein the IF amplifier has an operating bandwidth from around DC to around 350 MHz 31. A circuit according to any one of clauses 18 to 30, wherein the circuit is configured to operate within or around an X-band frequency range, for example from 8.8 to 9.8 GHz. 32. A circuit according to any one of clauses 18 to 31, wherein the circuit has a power rating of around 100mW or less.33. A circuit according to any one of clauses 18 to 32, wherein the circuit is configured to operate with a measured spin sensitivity of about 7x107spins / Hz1 / 2on a sensitive volume of about 0.1 nL. 34. A circuit according to any one of clauses 18 to 33, wherein the circuit includes one or more filters.

[0096] Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention. Although the specification describes using the disclosed ESR microsystem for performing pulsed ESR spectroscopy, the ESR microsystem may additionally or alternatively be used for performing continuous wave ESR spectroscopy. Although the disclosed ESR microsystem is integrated onto a single chip, more than one chip may be used in alternative embodiments. Or the microsystem may be replicated several times on the same single chip for parallel (simultaneous) ESR spectroscopy of several

[0097] The presence of " / " in a FIG. or text herein is understood to mean "and / or" unless otherwise indicated, i.e., “A / B” is understood to mean “A” or “B” or “A and B”. The recitation of a particular numerical value or value range herein is understood to include or be a recitation of an approximate numerical value or value range, for instance, within + / - 20%, + / - 15%, + / - 10%, + / - 5%, + / - 2.5%, + / - 2%, + / - 1%, + / - 0.5%, or + / - 0%. The term "essentially all" or "substantially" can indicate a percentage greater than or equal to 50%, 60%, 70%, 80%, or 90%, for instance, 92.5%, 95%, 97.5%, 99%, or 100%.

[0098] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0099] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or groupof integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

CLAIMS:

1. An electron spin resonance (ESR) microsystem, including: one or more microcoils, a first and second amplifier, and a mixer, wherein the one or more microcoils, the first and second amplifiers, and the mixer are located on a single chip, and wherein the microsystem is suitable for performing pulsed ESR spectroscopy on a test sample positioned at or near the one or more microcoils by being configured to perform the steps of: producing a magnetic field in the one or more microcoils, generating one or more ESR signals in the one or more microcoils based on a response of the test sample to the magnetic field produced by the one or more microcoils, amplifying, using the first amplifier, the one or more ESR signals generated by the one or more microcoils, down-converting, using the mixer, the one or more amplified ESR signals amplified by the first amplifier, and amplifying, using the second amplifier, the one or more down-converted ESR signals down-converted by the mixer.

2. An ESR microsystem according to claim 1, wherein the microsystem is a single chip integrated ESR microsystem or part thereof.

3. An ESR microsystem according to claim 1 or 2, wherein the one or more coils is coupled to the first amplifier.

4. An ESR microsystem according to any one of the previous claims, wherein the first amplifier is coupled to the one or more coils, and the mixer.

5. An ESR microsystem to any one of the previous claims, wherein the first amplifier is located between the one or more coils and the mixer.

6. An ESR microsystem according to any one of the previous claims, wherein the mixer is coupled to the first amplifier and the second amplifier.

7. An ESR microsystem according to any one of the previous claims, wherein the mixer is located between the first amplifier and the second amplifier.

8. An ESR microsystem according to any one of the previous claims, wherein the second amplifier is coupled to the mixer.

9. An ESR microsystem according to any one of the previous claims, wherein the first amplifier is a low noise amplifier (LNA), optionally an X-band LNA.

10. An ESR microsystem according to any one of the previous claims, wherein the mixer is a double balanced mixer (DB-mixer).

11. An ESR microsystem according to any one of the previous claims, wherein the second amplifier is a low frequency (LF) amplifier or an intermediate frequency (IF) amplifier.

12. An ESR microsystem according to claim 11, wherein the IF amplifier has an operating bandwidth from around DC to around 350 MHz 13. An ESR microsystem according to any one of the previous claims, wherein the microsystem is configured to operate within or around an X-band frequency range, for example from 8.8 to 9.8 GHz.

14. An ESR microsystem according to any one of the previous claims, wherein the microsystem has a power rating of around 100 mW or less.

15. An ESR microsystem according to any one of the previous claims, wherein the microsystem includes one or more filters.

16. An ESR microsystem according to any one of the previous claims, wherein the microsystem is configured to operate with a measured spin sensitivity of about 7x107spins / Hz1 / 2on a volume of about 0.1 nL or less.

17. An ESR microsystem according to any one of the previous claims, wherein the chip and / or microsystem is around 1mm2or less in area, and optionally around 0.7 mm2in area.

18. An ESR microsystem according to any one of the previous claims, wherein the one or more microcoils includes an excitation microcoil and a detection microcoil.

19. An ESR microsystem according to claim 18, wherein the detection microcoil, first amplifier, mixer, and second amplifier are electrically coupled together as an integrated ESR receiver circuit.

20. An ESR microsystem according to claim 19, wherein the excitation microcoil is co- integrated with the integrated ESR receiver circuit.

21. An ESR microsystem according to any one of claims 18 to 20, wherein the excitation microcoil and detection microcoil are located on the same plane.

22. An ESR microsystem according to any one of claims 18 to 21, wherein the exciation microcoil and detection microcoil are concentric.

23. An ESR microsystem according to claim 21 or 22, wherein the detection microcoil is smaller in diameter than the excitation microcoil.

24. An ESR microsystem according to any one of the previous claims, wherein the ESR microsystem is further configured to perform one or more of the following steps of: • receiving the test sample at or near a first microcoil and / or a second microcoil, • producing a magnetic field in the first microcoil, and• inducing a current in the second microcoil based on the produced magnetic field of the first microcoil.

25. A method of performing electron spin resonance (ESR) spectroscopy with an ESR microsystem according to any one of the previous claims.

26. A method of performing electron spin resonance (ESR) spectroscopy with an electron spin resonance (ESR) microsystem comprising the steps of: placing a test sample at or near a detection microcoil, producing a microwave magnetic field in an excitation microcoil, inducing a microwave current in the detection microcoil based on the produced microwave magnetic field of the excitation microcoil, producing a microwave magnetic field in the detection microcoil based on the induced microwave current in the detection microcoil, generating one or more ESR signals in the detection microcoil based on a response of the test sample to the magnetic field produced by the detection microcoil, amplifying, using a low noise amplifier (LNA), the one or more ESR signals generated by the detection microcoil, down-converting, using a double-balanced mixer (DB-mixer), the one or more amplified ESR signals amplified by the LNA, and amplifying, using an intermediate frequency (IF) amplifier or low frequency (LF) amplifier, the one or more down-converted ESR signals down-converted by the DB-mixer.

27. A method according to claim 26, wherein the ESR microsystem includes the detection microcoil, excitation microcoil, LNA, DB-mixer, and the IF amplifier or LF amplifier.

28. A method according to claim 27, wherein the detection microcoil, excitation microcoil, LNA, DB-mixer, and the IF amplifier or LF amplifier are located on a single chip.

Images