Thin substrates are one of the possible choices to provide radiation hard detectors for future high-energy physics experiments. Among the advantages of thin detectors are the low full depletion voltage, even after high particle fluences, the improvement of the tracking precision and momentum resolution and the reduced material budget. In the framework of the CERN RD50 Collaboration, we have developed p–n diode detectors on membranes obtained by locally thinning the silicon substrate by means of tetra-methyl ammonium hydroxide etching from the wafer backside. Diodes of different shapes and sizes have been fabricated on 57 and 99 μm thick membranes. They have been tested, showing a very low leakage current (

Fabrication of PIN diode detectors on thinned silicon wafers

An original packaging method suitable for integrated thermal mass flow sensors is presented. The method is based on a polymethyl-methacrylate (PMMA) adapter, used to convey the fluid flow to the chip areas where the sensing structures are located. Sealing of the adapter was obtained by heating the chip itself to the PMMA glass transition temperature, in order to soften the adapter front surface and improve adhesion. The proposed approach was applied to the packaging of thermal flow meters obtained by post-processing standard integrated circuits. The resulting compact devices have been characterized by measuring the response to a nitrogen flow. Fabrication and testing of a very compact flow sensor is described.

A compact package for integrated silicon thermal gas flow meters

The invention relates to a method for the wet-chemical etching of a highly doped silicon layer in an etching solution. According to the invention, in order to be able to perform etching homogeneously, an HF-containing etching solution containing at least one oxidizing agent selected from the group comprising peroxodisulphates, peroxomonosulphates and hydrogen peroxide is used as etching solution.

Method for the wet-chemical etching back of a solar cell emitter

Two different architectures of integrated thermal flow meters based on a differential temperature configuration are investigated. A standard structure made up of a heater placed between two temperature probes has been compared to a recently proposed variant equipped with a double heater. The latter has shown a different dependence of the response on gas type when driven in a closed loop fashion. The possibility of using this architecture to compensate the intrinsic sensor offset has also been proposed. Devices have been fabricated by means of a simple and low cost postprocessing technique applied to chips fabricated with two distinct commercial processes. Postprocessing variants, imposed by the sophistication of modern processes, have been proposed and discussed. A compact gas flow sensor with the readout electronics integrated on the same chip has been fabricated and characterized. Experimental results on this device and new data on double heater structures have been discussed and compared with the reviewed data of previously presented devices.

Postprocessing, readout and packaging methods for integrated gas flow sensors

Greater than 60% of men (age 40+) are affected by lower urinary tract symptoms, furthermore, NIH has estimated that at least 10 million US men and women suffer from urinary incontinence. However, it is thought that these statistics grossly underestimate the actual prevalence of these types of illnesses. This can be partially attributed to inhibition of a patients’ voiding process if someone is watching them, which often leads to inaccurate results as well as sometimes avoidance of medical help altogether. There are a number of different urodynamic tests used to assess how well the bladder and urethra store and release the urine. These tests include measuring the urine flow rate, volume, pressure, leakage, frequency, urge to urinate, urine stream, pain level while urinating, and urinary tract infections. This paper discusses multiple Urodynamic methods including non-invasive, invasive, homebased, and identifies the gaps available in current technology. In addition, the paper presents the Guidelines for Urodynamics practices developed by the International Incontinence Society. Some urodynamic tests are simple where physicians listen to a patient while urinating to understand the pattern of urination. Other techniques involve inserting a catheter into the urinary tract to measure the internal pressure of the urethra and the volume of the urine. Current methods do not enable physicians to observe the urine stream because patients need to urinate in a private setup. This results in the loss of valuable diagnostic information present in observing the shape of the stream. A new system recently designed overcomes this shortcoming, however, it requires design modifications before it can be used for women. Non-invasive methods utilizing sensors used in clinical setup provide a good insight on the urinary track. However, invasive techniques are needed to identify causes of complicated problems in urinary track.

Critical Review of Uroflowmetry Methods

A microsystem composed of a micromachined resistive flow sensor and a signal conditioning CMOS IC is proposed for biomedical applications. The device can be adapted to noninvasively monitor urinary dysfunctions in male patients. The flow sensor, thermally simulated with ANSYS, is based on the hot-film principle: A thin film of gold laid on a suspended micromachined silicon membrane is heated while the fluid under test flows through the duct mounted above the membrane. The flow rate is sensed by measuring the temperature difference between two of the four polysilicon temperature sensors realized on the membrane. Simulations of the flow sensor with flow rates within 0.1-18 ml/s evidence a maximum temperature difference of 20degC between the temperature sensors. Characterization of the fabricated flow sensor shows temperature coefficient of resistance (TCR) values of -1930 ppm/degC for the polysilicon resistors, i.e., a resistance variation of about 4% at high flow rates. The CMOS readout designed for the flow sensor is a resistive bridge-to-duty cycle converter based on a relaxation oscillator. The digital output of the circuit is duty-cycle modulated by the change in resistance of the flow sensor's elements. Experimental tests on the CMOS interface, conducted with a setup of 1% precision resistors, report a maximum nonlinearity below 0.9% and a resolution of 7 bits over the full range of 4% resistance variation. The CMOS integrated readout circuit, provided with a digital output, allows simple signal interfacing towards any standard PC for periodical data transfer and storage

A low-cost microsystem for noninvasive uroflowmetry

Tetra-methyl ammonium-hydroxide-with-water solution, or TMAHW, is an anisotropic silicon etchant that is gaining considerable use in silicon micromachining as an alternative to the more commonly used KOH (potassium hydroxide) and EDP/EPW (ethylenediamine-pyrocatechol-water) etchants. This is mainly due to its excellent compatibility with CMOS processing, etch selectivity, anisotropy, and relatively low toxicity. TMAHW exhibits a high etch rate for lower concentrations of solutions; however, this rate falls dramatically due to the inevitable formation of hillocks on the etched surface. For higher TMAHW concentrations, hillock formation can be suppressed at the expense of lower etch rates. In this paper, an improved TMAHW solution, which incorporates an oxidizing agent additive producing higher etch rates and a better surface quality, will be examined and characterized. The influence of temperature and concentration of these TMAHW solutions is studied in order to optimize this anisotropic silicon etching procedure for its use as an efficient process step in the fabrication of microelectromechanical systems (MEMS).

Characterization of TMAHW silicon etchant using ammonium persulfate as an oxidizing agent

ELECTROCHEMICAL EFFECTS DURING ANISOTROPIC BULK-SILICON ETCHING WITH DOPED AND UNDOPED TMAHw SOLUTIONS

Nowadays MEMS device fabrication requires an accurate knowledge of silicon etching parameters. We studied the relation between thin film masking layers residual stress and the orientation dependence of the silicon etching rate using TMAH solutions. In particular we focused on widely used masking films such as SiO/sub 2/ and Si/sub 3/N/sub 4/. Dedicated test structures were designed, fabricated and tested. We found an influence of the masking layer residual stress on the silicon etching rate anisotropy and a lower value of anisotropy for higher stressed structures.

http://ieeexplore.ieee.org/iel5/8531/26945/01197364.pdf

V. Guarnieri

Papers

A low-cost microsystem for noninvasive uroflowmetry

Characterization of TMAHW silicon etchant using ammonium persulfate as an oxidizing agent

ELECTROCHEMICAL EFFECTS DURING ANISOTROPIC BULK-SILICON ETCHING WITH DOPED AND UNDOPED TMAHw SOLUTIONS

Influence of masking layer stress on anisotropic silicon etching in TMAH solutions

Ch4 infrared sensor system including a microheater and a thermopile