RU2035808C1 - Voltage-to-frequency converter - Google Patents

Abstract

FIELD: electrical and radio engineering. SUBSTANCE: voltage-to-frequency converter is manufactured in the form of multilayer structure composed of semiconductor substrate 1, dielectric layer 4, gate 5 and ground 7 metal electrodes. Semiconductor substrate carries high-resistance semiconductor layer 3 with opposite type of conductance which thickness does not exceed diffusion length of its minority carriers. Two low-resistance regions 2 of same type of conductance placed at distance not more than five diffusion lengthes of minority carriers are formed in high-resistance layer 3. Gate metal electrode 5 is located on dielectric layer 4 arranged on high-resistance semiconductor layer 3 between contact metal electrodes 6 positioned in low-resistance regions 2. High resistance semiconductor layer 3 includes deep and shallow dopes of opposite signs. Ratio of concentration of minority and majority carriers is greater than ratio of lifes of shortlived and long-lived charge carriers. EFFECT: enhanced operational stability and reliability. 5 cl, 1 dwg

Description

 The invention relates to devices for measuring currents or voltages, in which it is possible to indicate their presence or direction using the conversion of voltage or current into the frequency of electrical oscillations and measuring this frequency.

 Currently, in electrical engineering, digital DC voltmeters are widely used [1]. They use various primary voltage converters (sensors), the common disadvantage of which is that their output signal is analog. Therefore, the composition of digital voltmeters includes two mandatory nodes: an ADC that converts the output signal of the sensors into a digital code in accordance with the value of the measured value, and a digital reading device that reflects the value of the measured value in digital form. In particular, among digital voltmeters, the most common are integrating voltmeters in which the value of the measured voltage is first converted to the frequency of the electrical signal, which in turn is measured by a standard digital frequency meter. A common disadvantage of devices of this class is their bulkiness, which consists in the use of complex and expensive ADCs.

/df/dv/ 0,0093%B рабочая частота f_o 214 МГц.The closest technical solution to the invention is a device [2] made in the form of a multilayer structure consisting of a semiconductor substrate, a dielectric layer, a gate and earth metal electrodes. A piezoelectric layer with metal interdigital transducers on it is located on the dielectric layer. With their help, surface acoustic waves are excited in a piezoelectric. A measured voltage is applied between the gate electrode located on the piezoelectric layer and the lower ground electrode located on the back of the semiconductor substrate. In this case, a change in the elastic properties of the piezoelectric film and a change in the frequency of the transducer occur. To control it, a frequency oscillator circuit is used when an electric voltage converter is introduced into the feedback circuit of a high-frequency amplifier. The converter is characterized by the following parameters: relative sensitivity
α _f =

/ df / dv / 0.0093% B operating frequency f _o 214 MHz.

 The disadvantage of this device is the low relative sensitivity.

 The aim of the invention is to increase relative sensitivity.

 To achieve the goal, in the device in the form of a multilayer structure consisting of a semiconductor substrate, a dielectric layer, a gate and ground metal electrodes, a high-resistance semiconductor layer with an opposite type of conductivity with a thickness of no more than the diffusion length of its minority charge carriers is formed on the semiconductor substrate, in which two low-resistance are formed regions with the same type of conductivity located at a distance of no more than five diffusion lengths of minority charge carriers of the layer are closed The th metal electrode is placed on a dielectric layer located on a high-resistance semiconductor layer between contact electrodes located in low-resistance regions, the high-resistance semiconductor layer containing small and deep impurities of the opposite sign, and the ratio of the concentration of minority and main charge carriers is more than the short-and long-life ratio charge carriers.

 The device is illustrated in the drawing, which shows a semiconductor substrate 1, a low resistance region 2, a high resistance semiconductor layer 3, a dielectric layer 4, a gate metal electrode 5, a contact electrode 6, an earth metal electrode 7.

 The material of the high-resistance semiconductor layer is an epitaxial film of a semiconductor containing shallow and deep impurities of the opposite sign, and the ratio of the concentration of minority and major charge carriers is more than the ratio of the lifetimes of short- and long-lived charge carriers. It is known that in such a material, electric instabilities of the type of recombination waves are excited at electric fields of about 10 V / cm. In the electric circuit, consisting of a DC voltage source, a load resistor and the inventive device, connected via contact metal electrodes, sinusoidal self-oscillations of the sound frequency current occur, caused by the excitation of recombination waves. When a measured constant electric voltage is applied between a gate metal electrode and an earth metal electrode in a semiconductor high-resistance layer, due to the field effect, depending on the sign of the measured voltage, either enrichment or depletion of charge carriers of this layer occurs. As a result, the frequency of sinusoidal current oscillations changes. Thus, the measured voltage is directly converted to frequency. In this case, the device has greater relative sensitivity due to the lower main operating frequency. To instability in an epitaxial semiconductor layer, it is necessary that its thickness be not less than the diffusion length of minority charge carriers. Studies have shown that recombination waves are excited in a static domain of a strong field, the length of which does not exceed five diffusion lengths of minority charge carriers; therefore, the distance between low-resistance regions with contact metal electrodes is chosen to no more than its (domain) length.

 An example of a specific implementation.

< N_Zn< N_p
После процесса диффузионного отжига пленка двуокиси кремния удалялась. Удельное сопротивление кремния в процессе диффузионного отжига повышалось до значения 2^.10⁴ Ом^.см, а тип проводимости не изменялся. Концентрация и времена жизни носителей заряда составляли: n=3,1^.10¹¹ см-^3, p=2^.10⁸ см-^3, τ_n= 1,6^.10-² с, τ_p= 3^.10^-6 с. Затем проводилось пиролитическое осаждение пленки двуокиси кремния толщиной 0,1 мкм. Техникой фотолитографии формировались область этой пленки между контактными и окна в окисле для низкоомных областей. Последние области n⁺-типа проводимости создавались методом ионного легирования фосфором (доза 3000 мкКл/см², энергия 40 кэВ) через маску из алюминия толщиной 1 мкм, которая предварительно напылялась на пленку двуокиси кремния, с последующим некогерентным импульсным фотонным отжигом длительностью 5-20 с. Концентрация электронов в этих областях составляла 1^.10¹⁹ см^-3. Далее с обеих сторон пластины напылялся слой алюминия толщиной 1 мкм и техникой фотолитографии на лицевой стороне пластины формировались затворный металлический электрод и контактные металлические электроды на низкоомных областях, расположенные на расстоянии 200 мкм друг от друга. Это расстояние меньше пяти диффузионных длин неосновных носителей заряда высокоомного полупроводникового слоя, так как диффузионная длина составляет L_р 70 мкм. Далее следует операция скрайбирования пластин на кристаллы размером 1х1 мм², которые с помощью эвтектики золото-кремний сажались на ножку корпуса ТО-18.An epitaxial layer of n-type silicon doped with phosphorus, 50 μm thick with a resistivity of 20 Ohms ^. cm was grown on a silicon p ⁺ -type substrate doped with boron with a specific resistance of 0.01 Ohms ^. cm 300 microns thick. Silicon was thermally oxidized to a film thickness of silicon dioxide of 0.5 μm. Next, by doping from the vapor phase in the evacuated ampoules, silicon was doped with zinc, and the ratio

<N _Zn <N _p
After the process of diffusion annealing, the silicon dioxide film was removed. The specific resistance of silicon during diffusion annealing increased to a value of 2 ^. 10 ⁴ ohms ^. cm, and the type of conductivity did not change. The concentration and lifetimes of charge carriers were: n = 3.1 ^. 10 ¹¹ cm- ^3, p = 2 ^. 10 ⁸ cm- ^3, τ _n = 1.6 ^. 10- ^2, τ _p = ^3. 10 ^-6 p. Then, pyrolytic deposition of a silicon dioxide film with a thickness of 0.1 μm was carried out. The photolithography technique formed the region of this film between the contact and the windows in the oxide for low-resistance regions. The last regions of the n ⁺ -type of conductivity were created by the method of ion doping with phosphorus (dose 3000 μC / cm ² , energy 40 keV) through a 1-μm thick aluminum mask that was previously sprayed onto a silicon dioxide film, followed by incoherent pulsed photon annealing for 5–20 with. The electron concentration in these regions was 1 ^. 10 ¹⁹ cm ^-3 . Then, an aluminum layer 1 μm thick was sprayed on both sides of the wafer and a gate metal electrode and contact metal electrodes were formed on the low-resistance regions located at a distance of 200 μm from each other on the front side of the wafer using photolithography technique. This distance is less than five diffusion lengths of minority charge carriers of the high-resistance semiconductor layer, since the diffusion length is L _p 70 μm. This is followed by the operation of scribing the plates on crystals 1x1 mm ² in size, which, using a gold-silicon eutectic, were mounted on the leg of the TO-18 body.

 The device operates as follows.

An electrical circuit is assembled from a 20 V DC power supply connected in series, a 4.7 MΩ load resistor and a device according to the invention connected through contact metal electrodes. In the circuit, spontaneous sinusoidal current oscillations occur with a frequency of f _o 2.30 kHz and an amplitude of U _o 100 mV. When a measured DC voltage of 5 V is applied between the gate and earth metal electrodes, the current oscillation frequency changes, and if the sign of the measured voltage is "-", then Δ f 70 Hz. Thus, the measured voltage is directly converted to the frequency of the electrical signal. The converter is characterized by the following parameters: relative sensitivity α _f 0.61% / V, operating frequency f _o 2.3 kHz.

The voltage-to-frequency converter according to the invention, in comparison with the base object, which can be taken as a prototype, has the following advantages: greater relative sensitivity (0.61% / V instead of 0.0093% / V); smaller dimensions (1x1 mm ² instead of 10x2.5 mm ² ); lower operating frequency (2.3 kHz instead of 214 MHz), the absence of a high-frequency amplifier, which allows to simplify the electronic circuit for converting and recording the frequency output signal of the device.

Claims (5)

 1. A FREQUENCY VOLTAGE CONVERTER IN FREQUENCY, made in the form of a multilayer structure consisting of a semiconductor substrate, a dielectric layer, a gate and ground metal electrodes, characterized in that, in order to increase the relative sensitivity, a high-resistance semiconductor conductivity layer with an opposite with a thickness not exceeding the diffusion length of its minority charge carriers, in which two low-resistance regions with the same type of wire are formed property located at a distance of not more than five diffusion lengths of minority charge carriers of the layer, the gate metal electrode is placed on the dielectric layer located on the high-resistance semiconductor layer between the contact electrodes located in low-resistance regions, while the high-resistance semiconductor layer contains shallow and deep impurities of the opposite sign, and the ratio of the concentrations of minority and major charge carriers is more than the ratio of the lifetimes of short- and long-lived charge carriers.  2. The Converter according to claim 1, characterized in that silicon is used as a semiconductor.  3. The Converter according to claims 1 and 2, characterized in that zinc is used as a deep impurity.  4. The Converter according to claims 1 to 3, characterized in that phosphorus or arsenic is used as a fine impurity.  5. The converter according to claims 1 and 2, characterized in that silicon dioxide or nitride is used as the dielectric layer.