D. Manic

Integrated Hall-effect magnetic sensors

Integrated Hall magnetic sensors are used in automotive and computer industry. Their farther penetration into other applications is mainly hampered by the problems of switching noise and of offset and drift related to the packaging stress. The equivalent magnetic noise and offset can be dramatically reduced by integrating magnetic flux concentrators on the sensor chip. A promising way to eliminate the influences of packaging stress and temperature variations is to apply the self-calibration using an integrated coil.

Short and long-term stability problems of Hall plates in plastic packages

Thermal-mechanical stresses occur in plastic IC packages. These stresses affect Hall plate magnetic sensitivity via the piezo-Hall effect. In this paper the short and long-term stability problems of Hall plates encapsulated in SOP and TSSOP packages are considered. A sensitivity shift is observed when reflow soldering, temperature cycling, or humidity testing are performed. Moreover, this shift is not stable in time and a slow relaxation is observed. This parameter shift is seen as a serious reliability failure of the Hall plates. Sensitivity drift is related to packaging stress drift due to the viscoelastic flow of the molding compound. The normal in-plane stress drift is calculated from the high-accuracy magnetic measurements.

Temperature cross-sensitivity of Hall plate in submicron CMOS technology

The temperature coefficient of the current-related sensitivity of a Hall plate in submicron CMOS technology was measured. A zero-temperature-coefficient region was observed. A model of the temperature coefficient based on the freeze-out effect and the temperature dependence of the Hall scattering factor was developed. Using a Hall sensor in the observed zero-temperature-coefficient region may significantly improve its measurement accuracy. The additional, very high influence of mechanical stress, due to the piezo-Hall effect, on the temperature coefficient has been analyzed for two packaging techniques.

A method for spark rejection in ultraviolet flame detectors

A novel method is presented to render ultraviolet (UV) flame detectors insensitive to ignition spark radiation. The method involves isolating the signal due to the sparks from the UV sensor output and subtracting a DC signal proportional to it from the output of the flame detector sensor system. A practical demonstration of the method is given using a commercially available UV flame detector with the addition of an analog circuit to perform the necessary signal processing. A selectivity improvement to spark radiation of greater than 130 has been obtained. The method is robust in that it is independent of the distance between the light source and the flame detector and has been designed to work with different spark generators found on the market. The analog circuit is simple, requiring few components, thus ensuring rugged, fail-safe operation and low cost.

Microsystem for high-accuracy 3-D magnetic-field measurements

Abstract A new microsystem for very high-accuracy magnetic measurement of all three field components is presented. A single silicon die incorporating eight sensor devices is mounted on a support and then cut. This galvanic separation is essential, since the applied technology of vertical Hall devices yields very high-quality devices, but does not provide for the isolation. In this way perfect alignment of the sensing directions of the sensors is achieved. All sensors are arranged in such a way that their signals can be combined to represent the x , y and z components of the magnetic flux density in the centre point of the system. The active volume is about 2 mm × 2 mm × 0.2 mm and the precision of the alignment is higher than 0.1 °. Measurements of cross-current and cross-sensitivity between the two in-plane axes of an identical but uncut sensor prove the necessity of cutting for achieving an accuracy of better than 1‰.

Die stress drift measurement in IC plastic packages using the piezo-Hall effect

Abstract A method for encapsulation stress drift measurement based on the piezo-Hall effect is proposed. Accuracy of ±0.25 MPa for the sum of in-plane normal stresses is achieved. Using this method, the drift of die stress in IC plastic packages has been measured after temperature cycling. Stress relaxation with the time constant of about one day has been observed.

Integrated microsystem for blue/UV detection

A fully integrated sensor microsystem for blue/ultraviolet (UV) radiation detection is presented. The photosensitive part includes a 1-mm 2 blue/UV-selective stripe-shaped photodiode, which has maximal response in the short-wavelength range. A 15-times smaller infrared (IR) photodiode is added to compensate the parasitic photocurrent generated by the blue/UV photodiode in the IR range. Thus, a very high ratio of the responsivities at 420 nm and 1 μm of 1500 is achieved. A transimpedance amplifier with 1 GΩ feedback resistor followed by an inverter is integrated on the same silicon chip. The main features of the operational amplifier (op amp) are a low offset (<0.5 mV) and fail-safe operation. This sensor has a maximal responsivity of 150 mV/nW at A = 420 nm, corresponding to 44% quantum efficiency. The system has a noise equivalent power of 5 × 10 -13 W. The 2.2 mm 2 microsystem is realized in a standard CMOS 0.5 μm process without any post-processing step.

Integrated microsystem for blue/ultraviolet detection

A fully integrated sensor microsystem for blue/ultraviolet radiation detection is presented. The photosensitive part combines a blue/UV selective stripe‐shaped photodiode with a small compensation infrared photodiode. A transimpedance amplifier with 1 GΩ feedback resistor is integrated on the same silicon chip. The main features of the op amp are a low offset (<0.5mV) and fail‐safe operation. This sensor has a maximal responsivity of 150 mV/nW at λ = 420 nm, corresponding to 43 percent quantum efficiency. A ratio of the responsivities at 420 nm and 1 μm as large as 560 is achieved. The system has a noise equivalent power of 5 10‐13 W. The 2.2 mm2 microsystem is realized in a standard CMOS 0.5 μm process.

Persistent photoconductivity as a tool for monitoring oxide cluster concentration in silicon wafers

Abstract Many semiconductor devices rely on the so-called “denuded zone” of the silicon wafers. It is therefore essential to have a simple means to monitor the purity of this zone. It will be shown that persistent photoconductivity (PPC) can be related to the oxygen concentration in the wafer, and thus can be used to evaluate the quality of the denuded zone. A test structure was designed and the PPC measurements performed. They clearly indicate that the intensity of the PPC effect is roughly proportional to the amount of oxygen clusters in the wafer.

Influence of assembling procedure on IC parameters

In this paper we present a new test structure, consisting of an array of piezoresistors, for analyzing the influence of the packaging procedure on the stability of silicon IC device parameters. The test structure has been mounted onto the Printed Circuit Board (PCB) substrate. Bending of the substrate with the mounted chip has been performed. The results show that a special mounting technique, leaving the sensor area free standing, significantly improves the mechanical isolation of the sensor. Finite Element Method (FEM) simulations give us the same conclusions. Finally, stress induced effects on the test structure due to the wire bonding have been measured and a change of 0.8% in offset voltage in a Wheatstone bridge configuration has been reported.