High-ohmic Silicon Research Articles

Usage and Experimental Tests of the Modified Waveguide Method for Measurement of the Complex Permittivity and Permeability of Materials

Results of the numerical experiment are presented, which allow considerably extending the range of the waveguide method capabilities in determination of the complex permittivity of materials. Two main methodological errors are estimated, which affect the measurement accuracy and are related to errors in determination of the sample boundary positions in the measuring section and to presence of an air gap between the sample and the wide wall of the waveguide. Calculations are performed in the centimeter and millimeter ranges for materials with a large real component of the permittivity (e1 ⩾ 25) and tangents of the dielectric loss angle tan δe varying between 0.1 and 0.2. Ways of decreasing the errors are proposed. To decrease the measurement error caused by the inaccurate positioning of the sample boundaries, it is proposed to use measuring section-flanges with the length equal to the length of the sample. To decrease the error caused by the air gap between the sample and the wide wall of the waveguide, it is proposed to fill the gap with a nonconducting paste composed of finely dispersed copper powder mixed with petrolatum. The centimeter-range experiment on determination of the complex permittivity of high-ohmic silicon shows an appreciable decrease in the measurement error when the air gap is filled with the above paste. The presented method also allows the complex permeability of a material to be determined. The real component μ1 of the complex permeability of silicon as a dielectric is unity. This is experimentally confirmed.

The influence of edge effects on the determination of the doping profile of silicon pad diodes

Edge effects for square p+n pad diodes with guard rings, fabricated on high-ohmic silicon, are investigated. Using capacitance-voltage measurements of two pad diodes with different areas, the planar and the edge contributions to the diode capacitance are determined separately. It is found that the edge contributions are significant and that they strongly influence the determination of the doping concentration using capacitance-voltage measurements. After edge correction, the bulk doping of the pad diodes is found to be uniform within ±1.5%, which agrees with expectations. The edge-correction method is verified using TCAD simulations of two circular pad diodes with different radii.

Recombination in converters of β-radiation energy to electrical energy

β-to-electric energy converters based on high-ohmic silicon, as well as processes that provide a high conversion efficiency, have been studied. It has been shown that the conversion efficiency is related to recombination in the space-charge region of converters at low levels of injection. A technique for determining the parameters of recombination centers that is built on new conversion algorithms has been developed. These algorithms make it possible to change the monotonic (and exponential as a whole) current–voltage characteristic of the device to a singular curve and find the parameters of recombination centers. These parameters have been calculated in a wide temperature range. Regions in the temperature–forward bias coordinates have been revealed in which recombination fluxes are captured by a recombination center, which influences the saturation current of the current–voltage characteristic and the conversion efficiency.

Silicon Photodiode for Visible Spectral Region

Photodiodes with high sensitivity in the short-wavelength portion of the visible region of the spectrum, fabricated based on high-ohmic silicon, are widely used in scintillation devices for visualization of gamma radiation and x-radiation in nuclear physics and medicine [1]. The following have been used to improve collection of minority charge carriers generated by short-wavelength photons in the immediate vicinity of the silicon surface: a shallow p-n junction with a vertical [2] or a horizontal [3, 4] structure, a graded p-n junction formed by diffusion of boron through the lattice of a thin layer of silicon oxide on the substrate surface [5], and an inversion layer photodiode [6]. The use of an inversion layer photodiode is limited by the narrow range of linearity typical of the spectral responsivity. A general disadvantage of photodiodes formed by boron diffusion into n-type silicon is the presence in the near-surface layer of silicon of a barrier layer under the oxide, preventing electrons generated by light in the p-region of the silicon from crossing into the p-n junction [7]. Photodiodes based on n-p junctions formed by diffusion of phosphorus or arsenic are more stable in the short-wavelength portion of the visible region of the spectrum [8, 9]. Their sensitivity at O 1 [12]. This allows us to ensure the minimum depth for the non-photoactive zone on the silicon surface. Arsenic is selected because of the following considerations. Its low diffusion coeffi cient makes it possible to form shallow junctions. The depth of the arsenic-doped n-region in our case is 0.2 om. Due to the relatively low atomic weight and the similar size of the ionic radii for silicon and arsenic, mechanical strains arising when doping with arsenic are relatively small, which lets us decrease the number of defects in the n-region and reduce the effect of recombination processes compared with the phosphorus-doped n + -regions [13]. The ohmic contact to the n-region is formed on the periphery of the arsenic-doped n-region. A guard ring reduces the surface component of the dark current. It is designed to be combined with the ohmic contact to the substrate. The dimensions of the photosensitive region of the photodiode are 5 × 5 mm. A two-layer SiO2/Si3N4 antirefl ective coating is formed on the photosensitive surface of the n-i-p junction.

A Five-Band Reconfigurable PIFA for Mobile Phones

We describe the design of a small microelectromechanical systems (MEMS) switched planar inverted F antenna capable of operation in five cellular radio frequency bands. Both simulated and measured results are shown using MEMS devices fabricated in an industrialized process based on high-ohmic silicon. Results show that the antenna bandwidth (or size) and specific absorption rate can be significantly improved using such devices.

Microelectromechanical tunable capacitors for reconfigurable RF architectures

This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach.

DEPFET—a pixel device with integrated amplification

In the DEPFET pixel concept, the absorbed radiation directly modulates the channel current of a p-JFET transistor being integrated into a fully depleted high ohmic silicon substrate in every pixel cell, offering very low noise operation at room temperature. Hence, DEPFET pixels open new possibilities in biomedical applications, but also have a potential in particle physics and astrophysics. Second prototype 50 μm×50 μm single pixels as well as large (64×64) DEPFET matrices have been successfully produced and operated confirming the low noise behavior (12 e). Device studies as well as a full DEPFET pixel Bioscope system to be used in real-time digital autoradiography with excellent spatial and energy resolution for X-rays are presented.

The DEPFET pixel BIOSCOPE

The DEPFET pixel Bioscope system based on a DEPFET pixel matrix provides good spatial and energy resolution in real-time digital autoradiography. Due to its very low noise and a thin entrance window the online detection of tritium without vacuum or cooling is demonstrated for the first time. To achieve this milestone a p-channel junction field effect transistor on a fully depleted high ohmic silicon substrate (DEPFET) is used as unit cell for pixel detectors providing an excellent noise performance of 158 eV FWHM at 6 keV (12 e ENC) at room temperature (300 K). 64/spl times/64 DEPFET pixel matrices with square (50 /spl mu/m/spl times/50 /spl mu/m) or hexagonal (50 /spl mu/m/spl times/42 /spl mu/m) pixels have been developed and operated successfully. First measurements result in a homogeneous charge collection efficiency on the whole matrix area and a good linearity in the X-ray range from 5 keV to 60 keV. First images taken with the square and the hexagonal pixel matrices using an /sup 55/Fe-source as well as a 'proof of principle' experiment for online /sup 3/H-detection are presented and discussed.

A 36 cm/sup 2/ monolithic pn-CCD for X-ray detection on the XMM and ABRIXAS satellites

X-ray sensitive CCDs with outstanding properties have been developed and produced at the MPI Halbleiterlabor. They contribute to the focal plane instrumentation of two space missions: the European XMM and the German ABRIXAS satellites. These CCDs, presented here, use exclusively pn-junctions on ultra-pure, high-ohmic silicon for all active components, in particular for the transfer electrodes and the on-chip readout circuitry. Full depletion of the detector chip, a homogeneous and thin entrance window and large pixel sizes can be realized by this technological concept. This concept results in low noise performance, spectroscopic energy resolution, high detection efficiency, radiation hardness and fast readout. With these properties the so-called pn-CCDs ideally match the requirements of the satellites, which are given by the specifics of their X-ray imaging optics as well as the intensity, energy range and dynamic behavior of the objects to be observed.

New pixel detector concepts based on junction field effect transistors on high resistivity silicon

A p-channel Junction Field Effect Transistor on a fully depleted high ohmic silicon substrate (DEPJFET) has been used as unit cell for pixel detectors. The most important features of this structure are the internal charge amplification, the low power consumption and the low detector capacitance leading to a high signal to noise ratio. Two different prototype designs, featuring pulsed or continuous reset, have been fabricated and tested. Both have been characterized with respect to their signal performance and noise behavior.

Characteristics of an experimental batch of microstrip detectors

Characteristics of an experimental batch, consisting of 18 microstrip detectors, are presented in this article. The process of production and the properties of high ohmic silicon used for the detectors are briefly described as well.

Experimental detector chip for soft X-ray applications

In this paper an experimental chip is presented, which is made of high-ohmic silicon, containing both nuclear radiation detectors and transistors. The detectors have a two-dimensional position resolution and were fabricated according to two different multiplexing principles. The first principle is the capacitor-resistor multiplexing technique, which is superior with respect to crosstalk. The second principle is the capacitor-interconnect technique, which is superior with respect to energy measurement. The transistors were fabricated and operated under the same circumstances as the detectors and performed well. The measured parameters ( g m C gs = MHz–8 GHz ) indicate that these transistors are well suited to preamplification and multiplexing purposes. The combination of the presented detectors and transistors for soft X-ray measurement is a very good one, because the limited spatial resolution allows enough chip area for the integration of readout electronics and, when backside illumination is applied, the transistors are shielded from direct irradiation. Therefore it is concluded that the detector matrices and the transistors presented in this paper are well suited to the construction of detector matrices with on-chip signal processing for soft X-ray applications.

A novel diffusion-based silicon nuclear radiation detector

Abstract This paper presents a new type of silicon nuclear' radiation detector, in which the collection of generated charge carriers is established by means of diffusion instead of drift. This results in the omission of high-ohmic silicon, in a large reduction in bias voltage and in a very simple fabrication process. Calculations and experimental results demonstrate that different kinds of nuclear radiation can be detected and that a certain energy resolution can be obtained in particle measurement. The diffusion-based silicon nuclear radiation detector is well suited for counting applications, imaging and also, in the case of particles, for calorimetric measurements.

Contactless lifetime measurement in processed and preprocessed high-purity silicon radiation sensors

Abstract A contactless microwave method is presented for the measurement of the recombination lifetime of free carriers in high-ohmic silicon wafers (4 kω cm), which are used for the processing of (nuclear) radiation sensors. It is shown that the bulk lifetime can be measured following processing steps independent of surface parameters, when the intensity of the light source is kept low. The results of the measurements carried out by this method are compared with the results obtained by leakage current measurements. Good agreement is observed between the results.

Integrating transistors on high-ohmic silicon

Abstract This paper presents a compatible technology for integrating both radiation detectors and transistors on the same high-ohmic silicon substrate. Using this technology, chips have been fabricated containing a number of test transistors (MOSFETs) with different geometries. Measurements on the devices showed a threshold voltage between 0 and -3 V, and a transconductance between 25 μA/V and 1.25 mA/V for aspect ratios between 0.7 and 50, respectively. The results demonstrate that transistors can be integrated together with radiation detectors onto one chip, which can lead to radiation detectors containing both detecting elements and signal-modification units, such as preamplifiers and multiplexers.

Monolithic integration of a nuclear radiation sensor and transistors on high-purity silicon

The physical operation of nuclear radiation sensors is briefly reviewed. A description is given of a typical experimental measurement-system setup, which can be divided into two parts: the application-specific part (including the detector and its associated electronics) and the computer-interfaced part (consisting of a multichannel analyzer). A number of recent improvements in the system design are discussed, and an extended description and a physical example are given of one of the most promising new ideas-the monolithic integration of both the radiation sensor and its associated electronics on one high-ohmic silicon substrate. The results proved to be a stimulus for making nuclear radiation sensors smart enough for direct digital input into computer systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

1193. High-ohmic silicon films obtained by submilation in vacuum on low-ohmic substrates: S P Svetlov et al, Electronic Industry, Scient-techn Coll, No 3, 1971, 46 ( in Russian)

1193. High-ohmic silicon films obtained by submilation in vacuum on low-ohmic substrates: S P Svetlov et al, Electronic Industry, Scient-techn Coll, No 3, 1971, 46 ( in Russian)