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In this work, we observe the distinct V TH characteristics in the Au-free gate-first processing p-GaN/AIGaN/GaN HEMTs with two commonly used passivation layers, i.e., SiN and SiO 2 . The device with SiN shows a depletion-mode (D-mode) characteristic (V TH ,. .., -5V) whereas the device with SiO 2 passivation exhibits an enhancement-mode (E-mode) characteristic (VTH, ..., +0.7V). Furthermore, Transmission Line Measurement (TLM) devices are fabricated to investigate the effects of the passivation on two dimensional electron gas (2DEG) in p-GaN/AIGaN/GaN stack. The results indicate that a low Rsh is obtained while passivating device surface with SiN layer, suggesting that 2DEG is present, which is most probably due to an unfunctional p-GaN layer. The SIMS results indicate a high H−intensity in the p-GaN/AIGaN/GaN stack with a SiN passivation layer. Thus, P-GaN deactivation due to the formation of complex Mg-H after SiN passivation is proposed to explain the D-mode characteristic in the device with a SiN passivation layer. more...

Accurate simulation and modelling is a very important aspect in designing a wearable antenna. In some cases, due to the complexity and non-homogenous properties of an electro-thread structure, the radiating element of the antenna is sometimes modelled as a perfect metallic surface, which is not the exact representative of the actual electro-thread and may cause deviation between simulation and measurement results. However, it is known that the exact fabric pattern and thread structure are very difficult to be physically modelled and designed. In order to reduce the uncertainties and the inaccuracy factors, the modelling of electro-textile in electromagnetic solver is reduced to bulk conductivity parameter of the radiating element. Therefore, an accurate method to measure the exact conductivity of a new or self-developed textile material, specifically for radio frequency application shall be determined. In this paper, a new technique is adopted to characterize the material’s electrical properties. This method is based on the measurement of scattering parameters, S21 of a two-port transmission line to determine the conductivity of any conductive textiles that are normally used in wearable antenna design. Here, the experiments were performed for two test samples; printed copper as the control sample and off-the-shelf conductive textile known as ShieldIt Super. Both samples were fabricated on a low-loss substrate, Rogers RO5880 having a very low dielectric loss of 0.0009 and dielectric constant of 2.2. The behavior and performance of these two samples operating at 2.45 GHz were investigated and studied in this paper through measurement and detailed simulation. As a result, the calculated conductivity derived from the theoretical transmission line equation based on the scattering parameter data and the substrate’s low-dielectric-loss-approximation was found to be very close to the expected conductivity values. Therefore, this method seems to be more reliable than the I-V curve measurement that was normally used for typical electronic application. However, specifically for radio frequency application, the reliability of the proposed technique shall be verified further especially in terms of its frequency range. more...

International audience; This work presents a comparative study of conventional and slow wave (SW) transmission lines implemented in an advanced 22-nm CMOS process. Both microstrip (MS) and coplanar waveguides (CPW) were analysed through simulations and measurements. A classical SW approach was used for the implementation of the SW CPWs while the SW effect was generated in the MS lines using bed of nails integrated in the CMOS process. As a proof of concept, the proposed SW MS approach was employed to design a new artificial quarter-wave TL section. The proposed configuration was created loading a meandered MS line with open ended S-MS stubs acting as discrete capacitive loads. Results show that the proposed methodology offers an attractive form factor and good performance. more...

The electrical performance of a photovoltaic (PV) module is greatly hindered by the existence of parasitic resistance losses, such as high series resistance (R s ) and low shunt resistance (R sh ). Contact resistance at metal grid/semiconductor interface and emitter sheet resistance are two major contributors to cell R s . Transmission Line Measurement (TLM) is a powerful method to estimate these resistance components. This paper presents the application of the TLM method to the cell strips extracted from field-aged PV modules at two different climates (Arizona and Florida) of the same design to investigate the influence of encapsulant material and microcracks on the contact resistivity and sheet resistance of the solar cell. The cells were initially extracted from the module laminate by dissolving the encapsulant polymer in trichloroethylene (TCE) solvent at 80oC for around 3 hours. The recovered cell was then used to cut into rectangular strips of 1.5 cm wide. The effective contact resistivity and emitter sheet resistance between two fingers in each strip were measured and compared to quantify the contact degradation induced from longer field aging. The Arizona module suffered from higher resistance as compared to the Florida module due probably to longer field exposure and higher operating temperatures. This method serves as a good diagnostic tool to anticipate and understand the severity of the contact degradation of solar cells in the fielded modules. more...

In this letter, the Metal-Insulator-Semiconductor (MIS) contacts are fabricated on the GaN substrates and compared to the Metal-Semiconductor (MS) contacts. To alleviate the Fermi level pinning effect at the Metal-Semiconductor interface, an Al 2 O 3 interfacial layer (IL) (1 ~ 3 nm) is used to form the MIS contacts. By comparing the electrical characteristics, the contact with 0nm Al 2 O 3 layer, i.e., MS contact, shows a lowest current compared to the contacts with an Al 2 O 3 IL, i.e., MIS contact. Furthermore, the current at 0.5V in the fabricated Transmission Line Measurement (TLM) device with 1nm Al 2 O 3 IL is 103 times higher the one without an Al 2 O 3 IL. This proves that inserting an Al 2 O 3 IL could mitigate the Fermi level pinning, resulting in a low Schottky barrier height. Finally, based on the TLM analysis, the resistivity of 5.1×10−4 Ω.cm2 is demonstrated in the MIS contact with 1nm Al 2 O 3 IL. more...

Thin film crystalline silicon (c-Si) solar cells have been a potential candidate to reduce the capital expenditure associated with traditional silicon photovoltaic market. This paper presents the sputtered NiO$_{\mathbf {x}}$ to be a potential candidate as hole-selective layer for c-Si solar cell contacts. NiO$_{\mathbf {x}}$ has a very small valence band offset (VBO $) ( \sim 0.1$ eV) and a large conduction band offset (CBO) with Si $( \sim 2$ eV), which makes it a promising candidate for hole-selective interlayer materials to reduce the contact recombination. In this paper, the effect of annealing condition on the NiO$_{\mathbf {x}}$/Si interface quality is first evaluated by Hall resistivity measurement. Also, the transport of both majority and minority carriers due to NiO$_{\mathbf {x}}$/Si band alignment is investigated by transmission line measurement. Results in this paper show that the sputtered NiO$_{\mathbf {x}}$ can be an effective interlayer material for thin film c-Si solar cell contacts. more...

We present the characterization of amorphous silicon/aluminum carrier-selective contacts in both front- and rear-emitter configurations, where the aluminum makes direct contact with the doped a-Si:H layers in silicon heterojunction solar cells. The resistance and passivation quality of these contacts have been measured using the transmission line measurement and the quasi-steady-state photoconductance techniques, respectively. The thickness of the doped a-Si:H layer in direct contact with the aluminum is 20 nm and post-aluminumsputtering annealing temperature ranges from 150-240 °C. Samples with aluminum on an a-Si:H(n) layer annealed at 180°C had a contact resistivity below 1 mΩcm2 while the lifetime remained at 4.8 milliseconds– essentially unchanged from the pre-sputtered, passivated sample. These values are superior to those for the traditional silicon heterojunction contact with a transparent conductive oxide layer and can enable devices with low resistive losses and tremendous optical properties through the insertion of a low-refractive index dielectric material at a wellchosen contact fraction. more...

The Nicolson-Ross-Weir (NRW) method is a classic technique for the measurement of complex permittivity and permeability of materials at RF and microwave frequencies. The method is based on the measurement of transmission and reflection coefficients of the material under test and subsequently, extracting the material parameters through a non-linear inversion process. The NRW method has a limitation on the thickness of the sample to be less than λ/2. The Stepwise NRW method that relies on seeking the correct branch in the inversion process, overcomes the limitation on the thickness on the sample. Both the methods rely on the reflection and transmission coefficients, which is obtained from two-port S-parameters measurements, by inserting the material under test inside a transmission line. In this work, a coaxial airline is used for the transmission line measurement. The de-embedding of the S-parameters, to obtain the reflection and transmission coefficients, requires the position/location of the sample inside the coaxial airline. This can potentially introduce errors due to position uncertainties. We propose a technique to estimate the position of the material under test inside the coaxial airline that eliminates inaccuracies due to positioning errors in the extraction process. The proposed technique relies on the symmetry of S-parameters to estimate the errors in the position of the material placed inside the coaxial airline. Subsequent de-embedding of S-parameters is performed taking into account the estimated error in the position of the material under test. Measurements and investigations are performed using both the NRW and stepwise NRW techniques illustrating the improvement in the accuracy of the measured material parameters. more...

We show a method for making a self-aligned selective emitter by annealing aluminum grid lines above the SiAl eutectic temperature, and study the recombination properties using lifetime measurements. The dark saturation current density at the metal contact (J0,metal) is determined as a function of minority carrier density using photoconductive decay. After annealing at 600 °C, J0,metal decreases from 1800 fA cm-2 to 500 fA cm-2 at an injection level of 1E15 cm-3. This value of J0,metal would correspond to a very low emitter recombination contribution of ~10 - 25 fA cm-2 for a front metal grid with area coverage of 2 - 5%. In addition, J0,metal is found to be injection dependent. A low contact resistivity of ~0.1 mOhm cm-2 is obtained from transmission line measurement (TLM). more...

The effect of self-heating and polarisation is studied in AlGaN/GaN Transmission Line Measurement (TLM) structures with varying the contact spacing between the source and drain. The measurement results of the I-V characteristics are calibrated and investigated by TCAD Atlas-Silvaco. The self-heating simulations show a hotspot at the vicinity of the drain side. The electrical stress that is applied on the Ohmic contacts decreases the polarisation as the source-drain distance is reduced, causing the inverse piezoelectric effect. more...

Thin film crystalline silicon (c-Si) solar cells have been a hot topic of photovoltaic research recently because its lower material consumption could potentially lead to lower capital expenditure. However, contact recombination is more prominent in thin-film c-Si solar cells compared with it in traditional c-Si solar cells due to higher carrier concentration. To address such a challenge, this work presents a design of metal-insulator-semiconductor (MIS) contact, based on thin TiOx layer that is grown by atomic layer deposition (ALD). Transmission line measurement (TLM) was conducted to study the conducting behavior of the TiOx MIS contact structure. Experimental results demonstrate that with the same doping density in silicon, the TiOx MIS contact forms an Ohmic contact to n-type silicon with good conductivity while cannot form Ohmic contact with p-silicon. This result demonstrates that the ALD TiOx layer can conduct electrons while blocking holes, thereby potentially reduce the contact recombination for thin-film c-Si solar cells, leading to an improvement of cell efficiency. more...

This paper reports the design and application of test structures for extracting the resistance of features formed when fabricating evaporated platinum (Pt) thin film structures on patterned, sputtered tantalum nitride (TaN). The combination of these two layers is used to produce an integrated resistive sensor structure. Two resistive features were considered during the test structure design: firstly the contact resistance between the two metal layers and secondly, the additional resistance introduced in the upper metal layer due to step coverage effects. more...

In this paper, a new de-embedding technique based on open-pad and Transmission Line (TL) measurement is discussed. This technique can be used as an alternative to the conventional de-embedding approaches in order to characterize on-chip passives in the millimeter wave range of frequencies. Using open-pad measurement, parallel parasitics are extracted and removed in the first step. Cross-talk parasitics between two pads that are kept at a constant distance can be assumed constant, and thus both cross-talk and parallel parasitics can be removed. Subsequently, the transfer function matrix of a single-ended TL is used to de-embed series parasitics from the measurement results. The measurement results are in a close agreement with the simulations up to 110 GHz. more...

We analyze three accurate broadband techniques for measuring the complex permittivity of dielectric substrates using coplanar waveguide transmission-line measurements and demonstrate good agreement with single-frequency cavity measurements. more...