Trap Level Distribution Research Articles

Thermoluminescence properties of β-ray irradiated LuAGG:Ce nanophosphors prepared by sol-gel method for potential applications in dosimetry

In this paper, Lu2.97Al5–xGaxO12:Ce0.03 (x = 0, 1, 2, 3) nanophosphors were synthesized using sol-gel method and calcined at 1100 °C for 3 h. The effect of Ga content on the structural, photoluminescence (PL), and notably thermoluminescence (TL) glow curve, dose response, repeatability and fading properties were investigated. X-ray diffraction (XRD) results indicated that all synthesized samples were crystallized in a pure garnet phase. The PL emission spectra exhibited a broad emission band corresponding to the 5 d → 4f (2F5/2, 2F7/2) transition of Ce3+ ions in the garnet lattice. Furthermore, a significant decrease in emission intensity was observed upon increasing Ga content. The TL characteristics of nanopowders irradiated with β-rays revealed a significant effect of Ga content on the peak position, shape and intensities of TL Glow curves, which can be explained by the reduction of the energy gap and the distribution of trap levels. The dose response linearity in the range of 0.125–100 Gy was examined for different Ga content, revealing a good linear behavior for x = 0 and 1 Ga. Additionally, samples prepared with x = 0, 1, and 2 Ga exhibited a high level of repeatability across a batch of 10 samples. Also, fading studies were performed for 128 h and revealed strong fading in samples synthesized with x = 0 and 1 Ga. These results suggest potential applications of Lu3Al5O12:Ce and Lu3Al4Ga1O12:Ce in ionizing radiation dosimetry.

Exploring beta irradiation responses in Sr2+-Doped hydroxyapatite: A thermoluminescence study

This research investigates the structural and thermoluminescence (TL) properties of Sr2+-doped Ca5(PO4)3OH (HAp) phosphors. X-ray diffraction (XRD) analysis confirms that HAp has a hexagonal structure with a P63/m space group. The TL behaviour of HAp:Sr2+ phosphors is examined under beta irradiation in the temperature range of 25–500 °C. The study reveals three TL glow peaks at temperatures of 75, 212, and 296 °C. Investigation of TL responses across heating rates (HR) ranging from 0.1 to 5 °C/s shows that higher HRs result in increased maximum TL peak temperatures and reduced TL intensities. This trend suggests an augmented contribution from non-radiative transitions as the heating rate increases. Importantly, no evidence of thermal quenching is found in the HAp samples. Two different methods, Hoogenstraaten's and Booth-Bohun-Porfianovitch, yield consistent activation energy values of 0.50, 1.22, 1.67 eV, and 0.48, 1.19, 1.63 eV, respectively. Reusability assessments indicate a standard deviation of less than 5 %, confirming the reliability of the materials. Tm−Tstop analysis reveals a continuous distribution of trap levels. TL properties in HAp samples have been comprehensively characterized, contributing not only to enhancing our understanding of their behaviour, but also highlighting their potential applications in various areas. The findings of this study have provided valuable insight into the development of efficient catalysts that are suitable for a variety of applications.

Facilitating Near-Infrared Persistent Luminescence in Cr3+ -Doped Gadolinium Gallium Garnets.

Near-infrared persistent luminescence (NIR PersL) materials provide great potential in the fields of night vision, biological imaging, and information encryption. However, among various crystal structures, Cr3+ -dopedgalliumgarnets show inferior PersL property, which turns out to be the bottleneck of their versatile applications. The rational design and facile preparation of high-performance NIR PersL materials are crucial for the emerging applications. In this work, a series of Gd3 Mgx Gex Ga5-2x O12 :Cr3+ (x = 0, 0.25, 0.5, 0.75, 1) is investigated by microwave-assisted solid-state (MASS) approach. Furthermore, by employing chemical composition co-substitution, PersL performance is further improved and the optimum working temperature is adjusted to the lower temperature at 10°C. Trap level distribution of Gd3 Mg0.5 Ge0.5 Ga4 O12 :Cr3+ phosphor is revealed based on the temperature and fading-time dependent PersL and thermoluminescence property. Further study demonstrates the reduction of the bandgap and the trap distribution forwards at shallow-lying trap energy levels. The synergistic effect, from both energy-band manipulation and trap-level optimization, facilitates NIR PersL in Cr3+ -doped gadolinium gallium garnets. These findings confirm the applicability of MASS-based bandgap and defect level engineering for improving the PersL properties in non/inferior-PersL materials. This burgeoning MASS method may facilitate a wide range of PersL materials for various emerging applications.

Charge carrier transport mechanism in plasma polymerized methyl acrylate thin films

Plasma-polymerized methyl acrylate thin films (PPMA) of thicknesses 115 to 290 nm were prepared using a capacitively coupled glow discharge plasma reactor. The current density-voltage (J-V) characteristics of the Aluminum/PPMA/Aluminum sandwich configuration were studied between 0.1 and 75 V over the temperature region from 298 K to 398 K for various thicknesses of PPMA thin films. J-V curves show that the conduction current follows Ohm's law in the low voltage area, but that in the high voltage range, the behavior is attributed to be space charge-limited conduction (SCLC) in PPMA thin films. The free carrier density, the trap density and carrier mobility have been determined to be around 1.77 × 1023 to 5.86 × 1023 m−3, 2.84 × 1024 to 3.77 × 1024 m−3, and 3.87 × 10−18 to 69.7 × 10−18 m2V−1s−1, respectively for various thicknesses of PPMA thin films. For the higher temperature and lower temperature areas, the activation energies were found in the range from 0.60 to 0.84 eV and 0.28 to 0.40 eV, respectively for 5 V in Ohmic region and from 0.61 to 0.98 eV and 0.27 to 0.34 eV, respectively for 60 V in SCLC (Non-Ohmic) region, respectively. It is observed that SCLC mechanism in PPMA thin films is dominated by a single dominant trap level/discrete trap level distribution. The PPMA thin films are promising candidates in manufacturing optoelectronic devices.

Unusual heating rates, dose responses and kinetic parameters detected on thermoluminescence from YAl3(BO3)4:Sm3+ phosphors

This study focused on the thermoluminescence (TL) characteristics of YAl3(BO3)4 (YAB) phosphors modified with various contents of Sm3+ ions. The TL response of the YAB: Sm3+ phosphors exposed to beta irradiation was measured across the temperature range of 25–500 °C, exhibiting three TL maxima at 70, 235, and 408 °C. Preheating protocol was also carried out to remove the low temperature TL peak followed by further experiments with the two-remaining high-temperature peaks. In the TL measurements conducted with variable heating rates (HR) between 0.1 and 5 °Cs-1, an anomalous heating rate behaviour was observed. A semi-localized transition model was used to address this feature. There was a standard deviation of less than 5% in the reusability measurements. The results of the kinetic parameters obtained by initial rise (IR) and various heating rate (VHR) methods were compared with those obtained by glow curve deconvolution (GCD) method. Tm-Tstop analysis revealed a continuous distribution of trap levels with a trap depth ranging from 1.35 to 2.20 eV. Through the use of GCD, the glow curve was found to demonstrate general order kinetics and consist of seven superimposed traps. The values of the kinetic parameters obtained for the glow curve agreed with those obtained by other methods excluding the VHR method encountering an anomalous impact. The results obtained from these tests showed that the sample could be successfully used for TL dosimetry applications.

Preparation and optoelectronic performance of 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine-CuS films for photovoltaic applications

This work intends to study the effect of the additional inorganic CuS layer between the ITO-contact and the organic 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (TTBTP). Two junctions of ITO/TTBTP and ITO/CuS/TTBTP were accomplished by the thermal vacuum evaporating technique. The capacitance-voltage characteristics of these two junctions were investigated. It was found that the built-in voltage was reduced from 0.62 to 0.35 V by the additional inorganic CuS layer. Further, the investigation of the dark current density versus the applied voltage at various temperatures emphasizes the influence of the adding inorganic CuS layer in the lowering of Rs , Rsh and n values. Moreover, getting the same value of the diode quality factor (n) at different temperatures for the two junctions suggested that thermionic emission is the adopted theory. Regarding the power-law (J ∼ Vm) relation, the charge transport mechanism is described by the space charge limited current controlled by a distribution of trap levels. The photoelectric study confirms that the additional inorganic layer plays a key role in the increasing of many parameters such as photosensitivity, short-circuit current density, open-circuit voltage, and power conversion efficiency. Increasing the conversion efficiency ten times by the additional inorganic CuS layer will open the doors for developing the fabrication solar cell with low cost, easily synthesized, and high conversion efficiency.

Impedance spectroscopy of amorphous/crystalline silicon heterojunction solar cells under dark and illumination

In this article, the electronic properties of a-Si:H/c-Si heterojunction (SHJ) solar cells are analyzed by performing impedance spectroscopy (IS) characterization in the dark and under controlled illuminations. Various dynamic electrical processes occurring at different time scales, ranging from microseconds to milliseconds, are observed mainly in the operating regime of the device. Several distinct characteristics are observed: a) time constant distribution characteristic of the disordered junction, b) typical bias voltage and illumination intensity dependence of the recombination time constant, and c) an additional time constant indicative of a fast process, which appears only under illumination. The impedance spectra of the SHJ cell are best modelled by including a dispersion element, the constant phase element (CPE), in place of a pure capacitor, in its small signal electrical equivalent circuit (EEC), aside from the pure resistive and capacitive elements arranged in a simple configuration. The CPE behavior is assigned to the complex small signal response originating from the distribution of trap levels in the disordered p+-a-Si:H/n-Si heterojunction. Under illumination, a distinct dynamic process is observed compared to the dark condition in the impedance spectra of the device. The variation of the dispersion parameter, resistances, capacitance, and time constants with external stimuli is discussed. In particular, the variation of the recombination time constant with bias is remarkable under different illumination intensities due to the change in the quasi-fermi levels splitting.

Current transport characterization and photovoltaic performance of Si nanopencil-based Schottky junction assisted with VOx as a hole-injection layer

Pencil-shaped silicon nanowires (SiNPs) were utilized in Schottky junction solar cells covered by sub-stoichiometric vanadium dioxide (VO2-x) to work as a hole injection layer. The asymmetry of nanopencils is responsible for their many useful properties, such as their ability to absorb and trap light over a wide spectrum. Dark current-voltage (I–V) curves for an Ag/VO2-x/SiNPs/Ti/Ag Schottky junction device were measured and analyzed across a temperature range of 298–358 K. The junction parameters were calculated in terms of thermionic emission theory at different temperatures from the (I–V) curves, including the ideality factor (n) and the barrier height (φb), and were found to be 1.73 and 0.78 eV, respectively, at room temperature. In the forward bias regime, we found that thermionic emissions dominate at low voltages (V ≤ 0.12 V), space-charge-limited current controlled by a single trap state dominates at middle voltages (0.12 < V < 0.3 V), and space-charge-limited current regulated by a distribution of trap levels dominates at high voltages (V ≥ 0.3 V). The (C–V) measurements were used to calculate the built-in potential, which was discovered to be 0.62 eV. Unless encapsulation is provided, PEDOT:PSS/SiNPs hybrid solar cells rapidly degrade under ambient conditions, whereas VO2-x/SiNPs solar cells are far more stable.

Defect characterization in Bi12GeO20 single crystals by thermoluminescence

Bi12GeO20 single crystal grown by Czochralski method was investigated in terms of thermoluminescence (TL) properties. TL experiments were performed for various heating rates between 1 and 6 K/s in the temperature region of 300–675 K. One TL peak with peak maximum temperature of 557 K was observed in the TL spectrum as constant heating rate of 1 K/s was employed. Curve fitting, initial rise and variable heating rate methods were applied to calculate the activation energy of trap level corresponding to this TL peak. Analyses resulted in a presence of one trap center having mean activation energy of 0.78 eV. Heating rate characteristics of revealed trap center was also explored and theoretically well-known behavior that TL intensity decreases and peak maximum temperature increases with heating rates was observed for the trap level. Distribution of trapping levels was studied by thermally cleaning process for different Tstop between 425 and 525 K. Quasi-continuously distributed trapping levels were revealed with mean activation energies ranging from 0.78 to 1.26 eV. Moreover, absorption analysis revealed an optical transition taking place between a defect level and conduction band with an energy difference of 2.51 eV. These results are in good agreement for the presence of intrinsic defects above valence band in Bi12GeO20 crystals.

Effect of mineral oil on flashover voltage of HTV silicone rubber under AC corona ageing: from the view of trap level distribution

The flashover voltage of high temperature vulcanised (HTV) silicone rubber will be decreased after corona ageing, and it further decreases under the effect of mineral oil. The mechanisms for the phenomena can be explained by considering the role of trap level distribution. In this study, the corona ageing of silicone rubber was conducted and the flashover voltage was tested. The isothermal surface potential decay was tested to explore the internal relationship between trap distribution and flashover voltage. Besides, the surface microtopography and chemical structure of silicone rubber were gained by scanning electron microscopy and Fourier infrared spectroscopy to explain the change of trap distribution. The test results show that the flashover voltage of HTV silicone rubber decreases with AC corona ageing time, the reduction of flashover voltage for an oil-impregnated sample is more serious. The density of shallow electron traps increases at first and then decreases, while the density of shallow hole traps increases with ageing time. The density of deep traps decreases after corona ageing. These trap level distribution characteristics are beneficial to promote the development of flashover, leading to lower flashover voltage. The effect of mineral oil can be regarded as an accelerated ageing effect.

Trap level distribution dependence of lifetime for polyimide films under repetitive impulse voltage

In this paper, polyimide (PI) films were modified by using non-thermal plasma, which was generated by dielectric barrier discharge (DBD) in atmospheric air. Under repetitive impulse voltage, the lifetime of plasma treated PI films increases obviously, which reaches the maximum value of 16.8% higher than that of untreated PI films, obtained by 20 s’ treatment. For further understanding lifetime improvement mechanism, energy level distribution of both electron-type and hole-type traps was calculated based on isothermal surface potential decay (ISPD) measurement. It is found that energy level of both shallow and deep traps decrease after treatment, reaching the lowest value for the films treated for 20 s. Lower energy for shallow trap is beneficial to charge dissipation, so that local electrical field would be mitigated. Furthermore, lower energy for deep trap results in less amount of trapped surface charges. Thus, surface PD intensity would be suppressed, ending up with longer lifetime. Analysis of chemical bonding structure reveals that active groups rich in oxygen and nitrogen were introduced into the near-surface region of plasma treated sample, which are responsible for corresponding change of trap energy level distribution. However, in order to prolong lifetime effectively, plasma treating time must to be controlled in an appropriate range.

Origins and effects of deep traps in functional group grafted polymeric dielectric materials

Introducing deep traps by grafting functional groups on molecular chains of polymeric dielectric materials has been proved as an effective way to improve their electrical properties, especially suppressing the space charge injection and accumulation. However, the underlying physical mechanism of the origins and effects of deep traps on the electrical properties of polymeric dielectrics has not been fully understood. In order to explore the origins and effects of deep traps in grafted polymers, both simulations of electronic band structures as well as 3D electric potential distributions at molecular level and experiments on the macroscopic trap level distributions are carried out. The simulation and experiment results reveal that the deep traps in grafted polymers originate from the different electronic band structures of the grafted polymer compared with the pristine polymer. The deep traps would capture charge carriers and inhibit the charge transport, which leads to decreased conduction current and suppressed space charge injection and accumulation. This work provides a deep understanding of the origins of deep traps in grafted polymers and their effects on the electrical properties, which may guide the rational design of high-performance polymeric dielectric and insulation materials.

Dielectric and space charge characteristics of nano-modified liquid silicone rubber for high-voltage DC cable accessories

In order to solve the problem of space charge accumulation in high-voltage DC cable accessories, nanometer titanium dioxide (TiO2) doping method is used to improve the space charge performance of liquid silicone rubber (LSR). Conductivity, dielectric spectrum and DC breakdown field strength, space charge distribution, and the trap level distribution of nano-TiO2/LSR composite samples were tested in this paper. With the increase of the doping concentration of nanoparticles, the DC conductivity increased, and the DC breakdown field strength decreased. The er of the TiO2/LSR composite sample increased with the increase in the doping concentration of nano-TiO2. As the frequency increased, tanδ decreased first in the low-frequency region and then increased in the high frequency. When the electric field strength increases from 10 to 20 kV/mm, the same polarity charges appear near the upper and lower electrodes of the sample, and the space charge accumulation doubled. After the addition of nano-TiO2, under the two electric field strengths, the space charge accumulation of 4 wt%-TiO2/LSR composite materials decreased by 24.55 nc and 81.03 nc, respectively. The trap energy level of the 4 wt% nano-TiO2 composites becomes smaller, and shallow traps are introduced, it was verified that the addition of 4 wt% nano-TiO2 particles reduced the space charge inside the composite sample and achieved the effect of suppressing space charge.

Influence of nitrogen ion implantation on surface charge accumulation and dissipation of polytetrafluoroethylene

To suppress the accumulation of charge on the surface of polytetrafluoroethylene (PTFE) material, radio frequency nitrogen plasma was generated to perform plasma immersion ion implantation (PIII) on the PTFE surface to improve its surface properties. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), water contact angle measurement, surface resistivity measurement and surface potential attenuation measurement were performed on the samples of PTFE material before and after injection to analyze the changes in surface composition and physical properties of PTFE samples after ion implantation treatment. Based on the theory of isothermal surface potential attenuation, the energy levels and density distributions of the surface traps were calculated. The results show that after nitrogen ion implantation, the main change in the chemical composition of the surface of the PTFE material is the destruction and conversion of its own molecular structure, and part of the CF2 structure is transformed into the CF and CF3 structures, resulting in shallower trap levels on the sample surface. The results also show that the water contact angle rose to about 140°, which is about 27° higher than that of the unprocessed sample. The surface resistivity drops to 3×1015 Ω, which is two orders of magnitude lower than that of the unprocessed samples. After 1 min of corona discharge on the surface, the amount of accumulated charge on the surface of the PTFE material processed with nitrogen ion implantation decreased, and the rate of dissipation increased. This is because the lower surface trap level is conducive to surface charge trapping, and the reduction in surface resistivity also promotes the dissipation process of surface charge along the surface. The curve of trap level distribution on the surface of PTFE sample also confirmed this.

Semi-Automated Extraction of the Distribution of Single Defects for nMOS Transistors.

Miniaturization of metal-oxide-semiconductor field effect transistors (MOSFETs) is typically beneficial for their operating characteristics, such as switching speed and power consumption, but at the same time miniaturization also leads to increased variability among nominally identical devices. Adverse effects due to oxide traps in particular become a serious issue for device performance and reliability. While the average number of defects per device is lower for scaled devices, the impact of the oxide defects is significantly more pronounced than in large area transistors. This combination enables the investigation of charge transitions of single defects. In this study, we perform random telegraph noise (RTN) measurements on about 300 devices to statistically characterize oxide defects in a Si/SiO technology. To extract the noise parameters from the measurements, we make use of the Canny edge detector. From the data, we obtain distributions of the step heights of defects, i.e., their impact on the threshold voltage of the devices. Detailed measurements of a subset of the defects further allow us to extract their vertical position in the oxide and their trap level using both analytical estimations and full numerical simulations. Contrary to published literature data, we observe a bimodal distribution of step heights, while the extracted distribution of trap levels agrees well with recent studies.

Radiological emergency dosimetry – The use of luminescent mineral fillers in polymer-based fabrics

Mineral fillers are widely used in the manufacture of thermoplastics and they are commonly found in the fabrics used to form bags. We show that carbonate mineral filler grains incorporated within faux leather fabrics and the coatings applied to woven nylon fibre fabrics exhibit a bright thermoluminescence TL response to ionising radiation dose, similar to that of calcite, with a broad thermoluminescence (TL) peak at 100 °C. The fabrics tested are shown to be potentially suitable as a surrogate material for emergency dosimetry, exhibiting a linear TL response to dose between 0.1 and 10 Gy, and with a detection limit varying with fabric type from 4 to 400 mGy. The region of the TL glow curve selected for dose evaluation was between ca 100–200 °C, and this is restricted by the presence of a native signal associated with the 250 °C TL peak. The rate of fading observed varied with glow curve temperature, attributed to the presence of a distribution of trapping levels; following 24 h storage at room temperature the loss recorded for the optimal glow curve temperature region selected (160–162 °C) ranged from 30 to 80 %, according to fabric and filler type. However, the fading mechanism is predominantly thermal and its rate can be substantially reduced by storing irradiated materials below room temperature. The use of filler minerals incorporated in the manufacture of plastics provides the scope to exploit a much wider range of materials for application to emergency dosimetry.

Thermal properties and space charge behavior of thermally aged polypropylene/elastomer blends nanocomposite

Polypropylene (PP)-based composites including PP/thermoplastic polyolefin (TPO) elastomer blends and PP/TPO-based nanocomposite are rather promising insulation materials for HVDC cables. Aging is an inevitable issue in practical operation and needs to be investigated thoroughly. In this paper, PP/TPO blends and PP/TPO/ZnO nanocomposite were prepared and thermally aged at 130 °C for various periods (28 days at longest). The micro-morphology, thermal properties and high-temperature space charge behavior were investigated. The results show that PP and TPO still exhibited excellent compatibility without phase separation after thermally aging. The crystallinity was not influenced after thermally aging, but a new endothermic peak at about 140 °C appeared in the melting process of thermally aged composites. Space charges accumulated in the two thermally aged composites, but dissipated slowly in PP/TPO, while dissipated rapidly first and then reduced in PP/TPO/ZnO nanocomposite. The calculated apparent charge mobility and trap level distribution based on space charge dissipation show that deep traps increased in aged PP/TPO, but decreased in aged PP/TPO/ZnO nanocomposite, which may be correlated with the chemical variation of thermally aged polymer matrix. The work may give a reference on the aging research of PP-based composite material for recyclable HVDC cable insulation.

Temperature gradient dependence on electrical tree in epoxy resin with harmonic superimposed DC voltage

Transient superimposed voltage, which is accompanied by a temperature gradient caused by Joule heat, can threaten the insulation safety of high-voltage direct current (HVDC) cable terminations. In this study, an electrical treeing experiment was conducted on epoxy resin with temperature gradient under harmonic superimposed DC voltage. The temperatures in the high voltage side and ground side were controlled by heaters within that maintained the range of 30 to 120 °C, while the DC voltage was ±12 kV. An isothermal surface potential decay (ISPD) experiment was used to obtain the trap level distribution. The effects of the temperature gradient and voltage polarity on the tree growth were depicted by the tree morphology, tree length and accumulated damage. The results show that the temperature gradient affects the tree structure and accelerates its growth. The tree growth rate has a nonlinear trend under an increased temperature in the high voltage side, and shows a steady increase under an increased temperature in the ground side. The positive voltage has a more obvious acceleration effect on the tree growth than the negative voltage does. A charge transport model is proposed to describe the tree behavior under a temperature gradient. The nature of the charge carrier accounts for the trap distribution and polarity effect. The local temperature rise and superimposed voltage pose a threat to the insulation safety, and more attention should be given to the operation of the electrical apparatus.

Improved Electric Field Distribution Within Bushing Insulation by EP/GO Nanocomposites With Reduced Temperature Coefficient of Conductivity

Field grading within the dry-type bushing insulation presents a major challenge for DC applications due to the highly temperature-dependent conductivity of the epoxy resin insulation. An electric field regulation method based on the epoxy/graphene oxide (EP/GO) nanocomposites with the reduced temperature coefficient of conductivity is proposed and investigated in this paper. DC conductivity of EP/GO nanocomposites with different loadings of 0, 0.05, 0.1 and 0.5 wt% at various temperature are investigated. Trap level distributions are characterized by the isothermal discharge current (IDC) method to clarify the conduction mechanism. Obtained results show that more shallower traps are introduced and the thermal activation energies of the nanocomposites are reduced by the GO nanoparticles, indicating that the temperature coefficient of conductivity of the nanocomposites is reduced. The improvement of electric field distribution within the bushing insulation under operating voltage is verified when the EP/GO nanocomposite with an appropriate content is employed, based on an established ±800 kV valve-side bushing for a converter transformer. However, more defects will be introduced by the GO fillers with excessive content (0.5 wt%), resulting in an obvious reduction of the DC breakdown strength.

Effect of thermal ageing on space charge in ethylene propylene rubber at DC voltage

To understand the space charge characteristics of ethylene propylene rubber (EPR) used in MV/HV power cables under thermal stress, the space charge profile is measured by the pulsed electro-acoustic method under 20 kV/mm at 120 and 160 °C. The complex permittivity and physicochemical properties at the different ageing stages are measured and analyzed for an understanding of the effects of thermal ageing on space charge characteristics. The trap properties of EPR during thermal ageing is calculated and analyzed based on the space charge decay model. The results show that both the ageing time and temperature can affect the space charge characteristics of EPR The space charge characteristics of EPR can be ascribed to the trapping sites caused by the complex chemical and physical structures during thermal ageing. Under the thermal oxygen process, the polar groups and ions increase because of the EPR molecular chain breakages, and the charge injection from the electrodes increases. Based on the decay model of space charge and isothermal decay current theory, the distribution of trap levels in EPR at different ageing stages is obtained. The trap distribution under different ageing process can be explained by the theory of trap filling.