Electrical, thermal and noise properties of platinum-carbon free-standing nanowires designed as nanoscale resistive thermal devices

Platinum-carbon (PtC) composite nanowires were fabricated using focused electron beam induced deposition and postprocessed, and their performance as a nanoscale resistive thermal device (RTD) was evaluated. Nanowires were free-standing and deposited on a dedicated substrate to eliminate the influence of the substrate itself and of the halo effect on the results. The PtC free-standing nanowires were postprocessed to lower their electrical resistance using electron beam irradiation and thermal annealing using Joule heat both separately and combined. Postprocessed PtC free-standing nanowires were characterized to evaluate their noise figure (NF) and thermal coefficients at the temperature range from 30 K to 80 °C. The thermal sensitivity of RTD was lowered with the reduced resistance but simultaneously the NF improved, especially with electron-beam irradiation. The temperature measurement resolution achievable with the PtC free-standing nanowires was 0.1 K in 1 kHz bandwidth.


Introduction
The diagnosis of micro-and nanoelectronic devices and systems often involves temperature measurements.There are tools for such measurements involving macroscopic device that provide sub-micrometre spatial resolution and reach the temperature resolution in the range of 1 × 10 −2 to 1 × 10 −1 K [1].
These methods include plasmon nanothermometry [2], nanothermometry in devices [3], levitating nanospheres [4], and defects in diamonds [5].The aforementioned techniques provide good quality and reliable results but involve sophisticated measurement setups and may be cumbersome in certain applications.
At the macroscale, the simplest temperature measurements are performed electrically with thermocouples (TCs) or various kinds of resistive temperature detectors (RTDs).RTDs have been of interest since the last century and have been continuously improved [6].Their miniaturization allowed for faster response time and sensitivity [7].
A common technique which uses electrical micro-or nanoscale electric temperature sensors for thermal properties assessment is scanning thermal microscopy (SThM) which can achieve sub 1 × 10 −1 K temperature resolution [8] while scanning the sample surface.There is a possibility of fabricating the thermally sensitive tip on SThM probe as a nanowire [9] which can benefit from high thermal sensitivity and achieve resolution of 0.5 K [10].Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
If the goal was just to measure the temperature in the nano-or microscopic device or system the nanoscale TC or RTD could be fabricated directly on it or incorporated in its design.In such case other aspect like for example spatial resolution or mechanical properties of temperature sensor are irrelevant.The localisation and dimensions of such nanostructure would determine achieved spatial resolution, the stability and calibration procedures would limit the the absolute accuracy, while the sensitivity and noise would limit the resolution.
Determination of the properties of nanosize RTDs is commonly done by their transfer to dedicated substrate in form of a nanobridge between two microthermometers [11], a bridge between two suspended membranes [12] or to a substrate with electrodes [13].
The transfer of the nanostructures is labour-intensive and complicated process.One of the methods by which such nanostructures which smallest dimension is in the order of tens of nanometers may be fabricated directly on the substrate is focused electron beam-induced deposition (FEBID) [14].
Scanning electron microscopy (SEM) is a tool for high spatial resolution and high-sensitivity, solid-state investigations [15,16].In the FEBID scheme, the investigated structure is immersed in the environment of a metal organic precursor.On the areas exposed to the electron beam, metalcontaining structures can be deposited [17].These bottom-up and mask-less deposition techniques are suitable for rapid prototyping of various devices and structures, as the deposition process is faster and more flexible than conventional microelectronics fabrication processes.The structures, which are formed as metal grains in a carbon matrix (Me-C), can be fabricated in the location defined with the resolution of a scanning electron microscope.The FEBID nanowires can be fabricated on suspended, 3D structured and/or solid substrates, which opens the possibility to manufacture a variety of sensing devices.
The FEBID process has already found applications in electronics, e.g. for contact deposition [18], modification of MEMS devices and integration of diamond microparticle with microcantilevers [19] or atomic force microscope functionalisation to improve the magnetic properties metrology [20].
For the FEBID process, the gas injection system needs to be added to a modified SEM chamber for metalloorganic compound delivery, and a specific user interface has to be implemented in the electron beam position control software.Metalloorganic molecules adsorb on the surface of the sample.Afterwards, the scanning electron beam generates secondary electrons (SE), which break the chemical bonds of the precursor and induce deposition of a nanogranular material composed of metal nanoparticles embedded in a carbon (MeC) matrix (figure 1(a)) [21,22].
The parameters of the deposition, such as scanning strategy, beam energy, dwell time and pitch, influence the shape of the deposited structure and characteristics of the material (electrical conductivity, density, purity, etc) [23,24].
FEBID deposition is often associated with the halo effect (figure 1(a)) [25,26].The decomposed precursor molecules adsorb on the substrate in the vicinity of the fabricated nanowires.As a result, these molecules contribute in a parasitic manner to the main electric properties of the device.To remedy that we propose using the 3D substrates (figure 1b).In this case, even if the Me-C molecules move to the substrates, their contribution to the overall transport phenomena through the nanowire is significantly reduced.
In standard FEBID technology, nanostructures are deposited on a solid substrate (figure 2(a)) [14,24,27,28].However, in this case, the transport phenomena are influenced by the substrate properties [29][30][31].Such influence is reduced if nanostructures are fabricated as free-standing nanowires (figure 2(b)), so from the sensing point of view, they should take advantage of the granular structure of the MeC materials [32,33].
The nanostructures possess relatively high electric resistivity in the as-grown state.The electric resistivity may be lowered using various postprocessing techniques, such as chemical treatment [23,33], electron beam irradiation and thermal annealing.
The change of the FEBID structure electrical properties is caused by a variation in its material structure.In the case of using the MeC P PtMe 3 precursor the deposited material is in the form of platinum nanocrystallites about 5 nm in size immersed in a carbon matrix.Electrical transport mechanisms in such materials are include the intergrain tunnelling and hopping [34].
The electron beam irradiation is a process commonly used method for FEBID structures modification.It changes both electrical and mechanical properties of the irradiated nanostructure [27,[35][36][37][38].The FEBID process is a non-ideal decomposition of precursor molecules and the deposited  material contains unwanted carbon content.By additionally irradiating the material with an electron beam, the ratio of fully dissociated molecules increases.This leads to a reduction in carbon content and the distance between platinum nanocrystallites [36,39].In some cases, purification of the material from carbon occurred with the assistance of O 2 and water, causing carbon elimination [40,41].
The thermal annealing of FEBID structures is usually done by elevating the temperature of whole substrate in vacuum or controlled gas atmosphere [24,42,43].But it is also possible to thermally anneal the FEBID structure by the self-heating due to the Joule heat generated by controlled DC current flow through the deposited nanostructure [44].
Material analysis after thermal annealing processes indicates a reduction in the carbon content of the composite, an increase in the size of the platinum grains, and therefore an enhancement of the intergrain tunneling ratio [34,35,42].When high temperatures, such as 900 °C, are used, metallic particles could precipitate on the surface, and carbon from the outer layers of the deposited material could be oxidized [45].Consequently, even a continuous metallic structure might be formed.In addition, annealing also affects the carbon matrix as the sp 2 fraction content increases and the carbon matrix becomes graphite-like structure [46,47].
The goal of the presented research was to evaluate the performance of PtC RTD nanostructures fabricated using FEBID technology with MeC P PtMe 3 precursor.Use of platinum mimics the typical RTD material for macroscopic sensors.To improve the reliability of the results RTDs were fabricated as free-standing nanostructures on 3D substrates which minimizes the influence of the substrate and halo-effect on the perceived electrical properties.We evaluate the temperature measurement resolution that is possible using free-standing PtC nanowires as a nanoscale RTDs.To do so we present the nanowire manufacturing technology, the measurement technology of the thermal, electrical and noise properties.We investigate the set of fabricated samples which differed with the post-grow processing methods at various stages of that process.According to our knowledge such evaluation was not reported before.

Substrates
The 3D substrates were fabricated using Si wafers with a thick SiO 2 layer, which was patterned using a combination of ICP and vapour HF etch with a Al 2 O 3 mask to achieve an insulating, sculpted structure.Its shape allowed the fabrication of separated and self-aligned Cr/Pd electrodes fabricated in the evaporation process [48].

Fabrication of PtC free-standing nanowires
Fabrication of PtC free-standing nanowires required the optimization of FEBID process to achieve straight, thin nanowires, preferably with small halo-effect and with specific length of 2.8 μm forced by the 3D substrate geometry.
Experiments presented in this work were conducted in the vacuum chamber of an FEI Helios NanoLab 600i FIB/ SEM system utilized as an SEM and FEBID tool.Freestanding nanowires were fabricated using the metalloorganic precursor MeC P PtMe 3 , which was introduced using a gas injector system (GIS).As a result, nanowires containing Pt grains with diameters ranging from 3 to 10 nm in the asgrown state embedded in the C matrix were fabricated [17,[49][50][51].
To optimize the fabrication process a set of PtC freestanding nanowires was deposited using the procedure described below.The electron beam was switched on and focused on the specimen.Next, the beam was blanked, the metalloorganic precursor was introduced to the chamber using a gas injection system (GIS) nozzle, and its concentration was stabilized.A set of vertical nanowires was then fabricated by focusing the electron beam in single spots for 10 s, 20 s, 30 s, 40 s and 50 s at various electron beam acceleration voltages of 2 kV, 5 kV, 10 kV, and 15 kV, respectively, and with currents at 0.086 nA, 0.17 nA, 0.69 nA, 1.4 nA, and 2.7 nA, respectively.After deposition, the GIS nozzle was closed, and the metalloorganic precursor was evacuated from the microscope chamber before imaging commenced.The resulting SEM micrographs (figure 3(a)) allowed us to determine the dimensions of the fabricated PtC nanowires.
This calibration procedure allowed us to determine the kinetics of the PtC free-standing nanowire fabrication (figure 4).The growth rate decreased with the wire length, resulting in a nonlinear relation between the deposition time and the wire height.Additionally, the growth rate decreased if the electron beam acceleration voltage or beam current was increased.
The optimal parameters were chosen based not only on the calibration but also on other parameters of the fabricated nanowires, such as their diameter and the presence of the halo effect [17].The diameter of the nanowires increased with the electron beam current.The halo effect was observed, especially in the vicinity of the structures fabricated with low acceleration beam voltages and high electron beam currents (figure 5).
Based on the performed experiments, an acceleration voltage of 5 kV, electron beam current of 0.17 nA and deposition time of 40 s were assumed to be the optimal deposition parameters (figure 4).
The PtC free-standing nanowires were deposited between the electrodes on the 3D substrate in a two-step process in which the sample stage was subsequently tilted by 45°and −45°(figure 3(b)).Special attention was paid to controlling the electron beam position and deposition time in a way that ensures that the ends of both nanowires met and provided good electric contact.Such process resulted in a PtC freestanding nanowire 2.8 μm long having 87 nm in diameter.

Electrical measurements setup
The 3D substrates were mounted on a resistively heated stage (figure 6).The stage temperature was measured with a Pt100 RTD placed in close proximity to the substrate on which the PtC nanowires were fabricated.The temperature was controlled with 0.01 °C resolution using a Eurotherm 3208 PID controller integrated with a custom power module, as shown in figure 7.
The electrical postprocessing and characterization of the PtC nanowires was performed using a Keithley 2602B source measure unit (SMU) providing voltage measurement resolutions of 1 μV and 10 μV in the 1 V and 6 V ranges, respectively, and current measurement resolutions of 1 pA, 10 pA and 100 pA in the 1 μA, 10 μA and 100 μA ranges, respectively.The postprocessing and electrical measurements were controlled with custom software.

PtC free-standing nanowire postprocessing
PtC material in its as-grown state exhibit relatively high resistivity.Two postprocessing methods were applied to lower the resistivity of the PtC free-standing nanowires: electron beam irradiation and thermal annealing by Joule heat self-heating.
Both methods were used to modify the properties of three nanowires marked as p2, p3 and p4.Nanowire p2 was annealed in three steps.In the first step, the DC current was gradually increased from 5 to 15 μA until the resistance was reduced approximately 10 times.In the second step, the current was increased up to 50 μA, which further reduced the resistance 10 times.The change in the structure resistance observed during the postprocessing steps is shown in figure 8(a).In the third step the p2 structure was irradiated for 600 s with a 0.17 nA electron beam, and the nanowire resistance was monitored using a small bias current of 5 μA.The details of the postprocessing and the resulting reduction of the nanowire resistance are summarized in table 1.
The P3 nanowire was irradiated with electron beam of 0.17 nA and 1.4 nA in the 1st postprocessing step and 2nd postprocessing step, respectively.The resistance change during the postprocessing presented in figure 8(b) was monitored using a small DC bias of 0.5 V.The last step of p3   nanowire postprocessing was annealing, during which the current flow was ramped up to 90 μA at 600 s.
The P4 sample was postprocessed by simultaneous annealing and electron beam irradiation.The bias current was increased to 10 μA in the first 200 s of the process, and then the electron beam was turned on and kept until the resistance dropped to approximately 100 kΩ, as shown in figure 8(c).

Noise measurements
The most convenient way to use PtC nanowires as temperature sensors is to bias them using a voltage source and to measure the current flowing through the nanowire.In this case, the current noise is the factor limiting the temperature measurement resolution.
The PtC free-standing nanowire noise properties were measured using a Keithley 2602B SMU.A constant voltage bias was applied, and 10 000 samples of the current at a rate of 10 samples per second were recorded.During the measurement, the structure was kept at a constant temperature of (30.00 ± 0.01) °C. Figure 9 presents the results of the exemplary measurements.
Next, the power spectral density (PSD) of the current noise was estimated by averaging the spectra of 1000 long-section samples of the measured data with the DC component subtracted and the Blackmann-Harriss window applied to minimize the influence of the spectral leakage.
Due to the sampling parameters, the spectra covered the frequency range from 10 mHz to 5 Hz.The observed noise PSD dependence on the frequency in that range was typical for the excess noise.The current noise PSD was then estimated in a wider range of frequencies by excess noise extrapolation and addition of the Johnson-Nyquist white noise of the nanowire.Both the measured PSDs and estimated PSDs are shown in figure 10.To ensure that the free-standing PtC nanowire PSD assessments were not affected by the measurement system noise, noise floor estimation was conducted by measuring the PSD of a metal-glazed resistor with resistance similar to that of the tested PtC free-standing   nanowire (4.7 MΩ).As shown (figure 10), the noise floor of the measurement system is significantly lower than the PtC nanowire PSD.
This wide-frequency range estimation was then applied to evaluate the RMS value of the current noise as a function of the upper frequency of the bandwidth f t by integrating its PSD starting at the frequency of 100 μHz.The lower bandwidth limit was arbitrarily chosen to correlate with the situation in which the temperature-sensing, PtC free-standing nanowire was employed to measure the temperature in an experiment lasting 1 hour.The dependence of the evaluated RMS current noise on the upper bandwidth frequency is also shown in figure 10.
The resistance of the fabricated, PtC free-standing nanowires changed significantly at various postprocessing steps, which caused changes in the mean value of the bias current during the PSD measurement and therefore the RMS value of the current noise.The noise figure (NF) is a convenient measure in such comparisons [52] and was evaluated as follows: where I DC is the mean value of the current resulting from the sample dc bias during the current noise measurement [53].

Thermal properties measurements
The thermal properties of the PtC free-standing nanowires were assessed while the temperature was changed in the following way: First, the temperature was set to 29 °C.After its stabilization, the ramp from 29 °C to 81 °C was started with the 5 °C per minute rate.During the temperature change, the fast I-V curve measurements were recorded at the temperature intervals of 2 °C starting from 30 °C.The I-V curve measurement took less than 1 s, which was fast enough to assume that the complete curve was measured at the same temperature.
The I-V curves were measured from the 0 V range to the 1.5 V range unless the resistance of the nanostructure was low enough to force the voltage range reduction to not exceed the 10 μA current.After reaching the 81 °C, the temperature was stabilized, and the ramp from 81 °C to 29 °C was initiated.The I-V curves were measured again in a similar fashion during the lowering of the temperature.Figure 11 presents the results of two exemplary measurements.
Usually, the temperature sensitivity of the RTDs is evaluated as the temperature coefficient of resistance (TCR).Unfortunately, the analysis of the I-V characteristic of the free-standing PtC nanowires (figure 12) shows that the freestanding PtC nanowires are nonlinear at their high-resistance state, which makes the direct resistance and TCR calculation impossible.
The temperature coefficients of the nonlinear component may be determined by the measurement conducted at a constant bias current: where V I 0@ B and V I 1@ B are the voltages measured at the bias current I B and temperatures T 0 and T 1 , respectively, or at constant bias voltage: where I V 0@ B and I V 1@ B are the currents measured at the bias voltage V B and temperatures T 0 and T 1 , respectively, as shown in figure 13.
As the values of TCC were greater in magnitude, this parameter was chosen as the parameter that characterizes the thermal properties of PtC free-standing nanowire.
All samples exhibited NTC-like behaviour, but it was observed that near room temperature, the temperature dependence of the current was practically linear, which allows us to evaluate TCC based on the linear approximation of the data recorded in the temperature range between 30 °C and 50 °C.
As many of the structures were not stable during the TCC measurement, the value that was taken for comparison was the TCC established during the temperature fall.To evaluate the temperature stability of the PtC free-standing nanowire, δI 30 was introduced and defined as: where I 30Z and I 30] are the currents measured at the bias point before the temperature cycle and after the temperature cycle, respectively (figure 11).
Taking into account the above equation, the resolution of the temperature sensing with the PtC free-standing nanowires

Results analysis
The results of the experiments are summarised in table 1; they describe the properties of the free-standing PtC nanowires operating as the RTDs.
As the PtC free-standing nanowires underwent consecutive postprocessing steps, the measured resistance is reduced.The resistivity of as-grown wires of about 1•10 6 μΩ cm is comparable with results from other groups [54] and is reduced down to several hundreds of μΩ cm which is just few times more than the lowest values reported for FEBID structures fabricated using MeC P PtMe 3 precursor [24].
The TCC of untreated samples was the highest at about 15 000 ppm K −1 .The postprocessing caused the resistance reduction of the PtC free-standing nanowires associated with the TCC decrease (figure 14).It was most significant for pure self-heating annealing process where it decreased to 1933 ppm K -1 for sample p2-2.At the same time samples p3-1 and p4-1, which have similar resistance, exhibit the TCC of about 5000 ppm K −1 .
If the resistance was lowered to tens of kΩ region the value of TCC was decreased to about 2500 ppm K −1 .This value was smaller than reported for PtC nanothermistor SThM probes [10].
The samples which postprocessing involved the electron beam irradiation showed almost linear relation between the TCC and the logarithm of the resistance was observed.Such result is in agreement with the previous reports.The irradiation doses were too small to pass the metal-insulator transition and achieve metallic-like temperature response [27,36].
The reduction of sensitivity seems to worsen the performance as the RTDs increase.However, the temperature measurement resolution depends not only on the sensitivity of the transducer but also on the noise, whose magnitude may be expressed as the NF.The values of NF calculated for the investigated samples are presented in table 1 and figure 15.
The relationship between free-standing PtC nanowire noise properties, the postprocessing method and its electrical parameters are complex.The results obtained for samples p3 and p4 show that it is possible to reduce the noise using electron beam irradiation alone or in conjunction with resistive heating.For the p2 sample, the noise properties significantly deteriorated after two resistive heating postprocessing steps.Afterward, the noise properties were partially improved after the third postprocessing step, which was electron beam irradiation (figure 15).
The aforementioned values may be expressed as the measurement temperature resolution ΔT (figure 16).
The analysis of the calculated results shows that it was possible to achieve 0.1-0.2K resolution for most of the samples, with the exception of the p2 sample after resistive annealing, in which the sensitivity reduction was not compensated for with the improvement of its noise performance.
In some applications of the RTDs, the additional factor that must be taken into account is their stability (figure 11).From that point of view, the best structures underwent annealing during resistive self-heating (p2 and p3 samples).
The overall evaluation of the RTDs based on the selfstanding PtC nanowires may be performed based on the analysis of their thermal resolution in situ the thermal stability plot presented in figure 17.
The best results of approximately ±0.5% stability were achieved for the p3-3 sample, which was annealed after  electron beam irradiation, and the p4-1 sample, which was simultaneously irradiated and annealed.
Note that the thermal stability of the p3 sample worsened after electron beam irradiation (p3-1), although the as-grown sample was thermally cycled before irradiation during the TCC measurement.

Conclusions
The presented thorough evaluation of the free-standing PtC nanowires employed as the nanoscale RTDs resulted in their electrical, thermal and noise characteristics.It may be the reference for further research on another FEBID materials as the measurement method was described extensively allowing for reliable comparisons.
The free-standing PtC nanowires in their as-grown state have provided quite good temperature measuring resolution despite poor noise performance due to their high sensitivity.Unfortunately, these PtC nanowires exhibit quite high resistance, which may be an inconvenience, and poor stability.
The experiments focused on the significant influence of the postprocessing method on their performance as the RTDs.Both methods resulted in reduction of the resistivity however their thermal and noise performance differed significantly.
In the applications where the ratio of the sensitivity to the noise is the most important, the electron-beam irradiation seems to be the best with a temperature measuring resolution of approximately 0.1 K.
If the thermal long-term stability is more important, then the annealing by resistive self-heating is more adequate as the postprocessing method.
The best overall compromise between temperature measurement resolution and stability was achieved when both methods were simultaneously employed.Proper choice of the manufacturing process of nanoscale RTDs based on the PtC nanowires is therefore essential.

Figure 1 .
Figure 1.Illustration of the FEBID process induced by the secondary electrons (SE) and the halo-effect on the flat (a) and 3D (b) substrates (drawing is not to scale).

Figure 2 .
Figure 2. Basic layouts of conductive FEBID nanostructures fabricated on substrates: flat structure deposited on the solid substrate (a) and free-standing nanowire (b).

Figure 3 .
Figure 3. SEM micrograph of (a) deposited series of PtC free-standing nanowires with different deposition times (the scale bar is 1 μm, and the stage is tilted); (b) a spatial, free-standing PtC nanowire connecting the two palladium electrodes on the 3D substrate (the scale bar is 500 nm, and the stage is tilted).Parameters of the deposition: 0.17 nA, 5 kV.The deposition time of the single nanowire was 30 s.

Figure 4 .
Figure 4. Height of the test PtC free-standing nanowires as a function of deposition time: (a) 5 kV acceleration voltage and variable e-beam current; (b) 0.17 nA current and variable e-beam acceleration voltage.The point related to the optimal deposition parameters is marked in green.

Figure 5 .
Figure 5. SEM micrograph comparison of PtC free-standing nanowires deposited in a time of 40 s.The electron beam parameters: (a) 86 pA and 2 kV; (b) 0.69 nA and 2 kV; (c) 2.7 nA and 2 kV (the scale bar is 500 nm, and the SEM stage was tilted by 45°).

Figure 6 .
Figure 6.FIB-SEM sample holder with the designed and fabricated heated stage (a) and integration of the 3D substrate holder with the FIB-SEM stage (b)

Figure 7 .
Figure 7. Simplified schematic of the fabrication and measurement setup of the free-standing PtC nanowires.

Figure 8 .
Figure 8. PtC free-standing nanowire postprocessing procedure.The p2 current flow postprocessing (a), p3 e-beam and current flow postprocessing (b) and sample p4 simultaneous current flow and e-beam irradiation (c) are shown.

Figure 10 .
Figure 10.Current noise power spectral density of the p4 sample.Shown are the calculated PSD (dots), simulated total PSD and Johnson-Nyquist noise PSD for the given nanostructure and the noise floor established by measuring the PSD of a metal glazed 4.7 MΩ resistor current noise.The simulated PSD was integrated from 100 μHz to evaluate the RMS current noise dependence on the bandwidth, as shown in blue.

Figure 11 .
Figure 11.Exemplary temperature property measurement results: the current change at constant voltage for p3-1 at 0.5 V and p2-3 at 0.2 V. Arrows denote the sequence of the measurements during the temperature cycle.I 30Z and I 30] are the current values at the bias point before and after the temperature cycle.

Figure 12 .
Figure 12.I-V curves of the p3 sample as grown (a) and at consecutive steps of postprocessing (b)-(d).

Figure 14 .
Figure 14.Temperature current coefficient versus the PtC freestanding nanowire resistance for all the tested samples (denoted as symbol shape and colour) and postprocessing steps (denoted as the symbol interior).

Figure 15 .
Figure 15.NF versus the nanostructure resistance for all the tested samples (denoted as symbol shape and colour) and postprocessing steps (denoted as the symbol interior).

Figure 16 .
Figure 16.Temperature sensing resolution ΔT versus the nanostructure resistance for all the tested samples (denoted as symbol shape and colour) and postprocessing steps (denoted as the symbol interior).

Figure 17 .
Figure 17.Temperature sensing resolution ΔT versus the thermal stability for all the tested samples (denoted as symbol shape and colour) and postprocessing steps (denoted as the symbol interior).

Table 1 .
Results of the electrical, thermal and noise measurements for all the tested samples as-grown and at all postprocessing steps.The resistance and resistivity at the operating point, temperature coefficient of current (TCC), temperature stability δI 30 , slope of the excess-noise approximation, RMS current noise, mean bias current, noise figure and temperature measurement resolution ΔT in 1 kHz bandwidth.