Sensors & Transducers e-Digest (S&TD)
No. 2, November 2000
Z - Sensors:
Semiconductor Multifunctional Sensors of Wide Range of Applications
New type of semiconductor structures with L-form current-voltage characteristic (CVC) were developed at the Institute of Control Sciences. A number of new phenomena which appear in semiconductor structures with CVC of L-form allow to design sensors of different physical quantities on its basis.
Functional and operational properties of such sensors absolutely surpass properties of all semiconductor sensors for the same application, such as Hall elements, strain gage elements, magnetic diodes, magnetic transistors, photo diodes, thermistors etc.
The structure principally consists of two regions having p- and n-types of conductivity. In each of these regions additional deep energy level impurities are diffusely implanted. These impurities change both its electrical properties and functions carried out by the structure. Different types of sensors were developed on the basis of such structures, which later were named Z-sensors after name of its inventor. Functional properties of Z-sensors are realized by goal-directed doping, compensation or overcompensation of basic material, increasing or decreasing of intensity of volume or surface recombination rate. By this it is succeeded to change technical and operational characteristics of Z-sensors depending on type of the injected impurity, its energetic interaction with basic material, impurity’s concentration and structures geometry.
In general case DC voltage applies to the structure (+ to p-region of the structure) via a load resistor R (Fig.1).
Ultra Violet Irradiation UV Z-sensors
Ultra violet Z-sensors are new semiconductor p-n structures with features of UV irradiation perception, accumulation of UV irradiation energy all along the exposition time and memory of accumulated dose 3-5 minutes. These functions can be realized by structure both in switched on and off position. To pick up the information (dose of accumulated UV irradiation) the structure must be connected to DC power source U with positive bias. Reminder of subtraction of initial current intensity (before UV irradiation) from final current intensity (after UV irradiation) will be proportional to the dose of UV energy accumulated during the exposition time. Recovery time (return to the initial current intensity) is 30-35 minutes after UV irradiation stop both in switched on and off power supply. Ultra Violet Z-sensors have not any analogs in the world.
Z-thermistors are intended for testing of pre-established temperature of any machines, biological objects, liquids and gases in the temperature range T from -30 to 100 degrees centigrade. They can be used also for linear measurements of temperature in three different ways of Z-thermistor’s operation. Z-thermistors are novel p-n structures with the function of transition from one stable state (weak current state) to another stable state (30-100 times bigger current state) when testing temperature mounts to pre-established level (temperature threshold). Adjustment of necessary temperature level can be easily realized by supply voltage U. Transient time is 1-2 microseconds. Circuit diagram consists of power supply source U and load resistor R, which serves to pick up output jump voltage (0.5-15 V without amplification).
Frequency Output Magnetic Z-sensor
The semiconductor p-n structures are sensitive to permanent and alternating magnetic field H directed perpendicularly to the current of structure. If the strength of magnetic field is lower than 30-50 mT Z-elements are operating in analog regime, i.e. output signal is DC voltage which picking up from load resistor R. If the strength of magnetic field exceeds 30-50 mT Z-elements generate pulses with repetition frequency proportional to the strength of magnetic field. Amplitude of output pulses are 30-40% of power supply voltage, i.e. in the order of some Volts without amplification.
Europatent #EP 0456825 A1
China #97113376 X and #972227361 IX.
For more information please order the following article:
Prof., D.Sc. Zotov V.D.
Russian Academy of Sciences,
Institute of Control Sciences,
VZ Sensor Co. Ltd.
Resistor R is used not only for picking-up an output signal and limiting the structure’s current, but under a number of conditions its value determines functional properties of Z-sensors. Generalized current-voltage characteristics of Z-sensors are presented at Fig.2.
Under absence of any external influence CVC has a form 1-2-3 with branch 2-3, which rise vertically if power supply U is increased. All properties and functional opportunities described below are displayed in structures of this CVC type in contrast to well-known S-type CVC. In the initial part of CVC (interval 0-1) current density is uniform for all square of the structure and is determined by the concentration of free current carriers in structure. During the pass of CVC from interval 0-1 to interval 2-3 current density is redistributed sharply during the time of 1-2 microseconds. Current density increases on small part of structure (< 0.3 mm2), while on the rest part of structure it decreases. Thus, microplasma or current filament is formed in the structure. It is similar to the described in literature current filaments in the structures with S-type of CVC, but physical mechanism of its formation and determined by it phenomenological properties are substantially different and is a result of current carriers pass from artificially implanted deep energy levels to the conductive band. Under certain ratio between current carriers concentrations in the zone of current filament (electrons) and p-region of the structure and necessary value of load resistor R following types of the stable state are possible in the structure (under absence of external influence):
1.Stable state with direct current at the interval 0-1 of CVC;
2.Stable pulse auto oscillations of current in the interval 1-2 with amplitude of up to 60% of applied voltage;
3.Voltage jump (transient time 1-2ms) from the point 1 into the point 3, with amplitude of up to 80% of applied voltage.
As it was mentioned depending on phenomenological composition of the structure and its construction physical properties of the structure and its sensitivity to the different external influences are changed. Sensitivity of the structures to the following external actions was revealed experimentally:
Also it seems possible to develop modifications of the structures, sensitive to corpuscular irradiation and gases which can change surface recombination.
Different intervals of CVC and their combinations can be used for development of sensors of these physical quantities. Besides, some external influences change form and parameters of CVC. Light irradiation and mechanical compression proportionally change frequency of auto oscillations in the interval 1-2. Magnetic field with intensity less than 50 mT, applied parallel to the structure’s plane proportionally changes voltage drop on the structure (interval 3-4) and magnetic field with greater intensities results in occurrence of pulse oscillations of current with frequency directly proportional to field’s intensity (interval 4-5 of CVC). So the structure converts analogue input influence ( magnetic field) into frequency-pulse output signal. Influence of UV radiation leads to the change of electrophysical parameters of the structure, which is expressed in time growing current rate across the structure (intervals 0-1 and 2-3 of CVC) e.g. conductivity of the structure changes, , thus in this case principle of charge accumulation is realized. After UV radiation switching off the finished value of structure’s conductivity and the current correspondingly is kept during some period of time (2-3 minutes) and after this the structure returns to the original state, e.g. memory function is realized. Also it is important that change of the structure’s parameters under UV irradiation is independent from power supply, e.g. take place without input of electric power, which in this case is necessary only for reading of the result of accumulation. Output signal of structures sensitive to thermal influence is a function of two quantities- applied voltage and temperature. Two regimes are possible: regime of measurements and regime of testing. Regimes of measurements can be realized at the intervals 0-1 and 2-3 of CVC, regime of testing of pre-established temperature is realized by using voltage jump 1-3 and the value of the testing temperature in this case can be given by simple change of applied voltage. On the base of described structures and phenomena in it at the Institute of Control Sciences in cooperation with VZ Sensor Ltd. company a number of Z-sensors have been developed.
Z-sensors have no analogous in world practice and according to their technical and operational characteristics absolutely surpass all known semiconductor sensors of the same purpose. Developed sensors do not need use of additional circuits of amplification, converting or conditioning of the output signal . Z-sensors are characterized with easy operation and low energy consumption. Their overall dimensions (1x1x0.3; 2x2x0.3; 5x2x0.3 mm) allow to use them in any hard to reach places or to design on its base different kinds of transducers.
Currently volume production of Z-sensors is realized by Chinese-Russian Joint Stock Company Harbin Noveike Sensor Co. Ltd. Following types of Z-sensors are supplied to the customers:
1.Semiconductor signal elements of pre-established temperature (Z-thermistors);
2.Magnetic sensitive Z-elements with frequency-pulse output signal.
3.Semiconductor measuring and accumulation sensors of Ultra Violet irradiation (UV Z-sensors).
4.Force sensitive Z-sensors.
5.Light sensitive Z-sensors with illumination threshold function.
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