SU1415086A2 - Semiconductor strain transducer - Google Patents

Abstract

The invention relates to a measurement technique and can be used to convert mechanical quantities into an electrical signal. The purpose is additional to auto speed. USSR No. 934257 of the invention — improving the accuracy of measurements over a wide range of temperatures. To do this, it is necessary to reduce the variation of the temperature error of sensitivity, due to the technological variation of hole concentrations in the strain gauge. Reducing the variation in temperature error is achieved by using its dependence on the ratio of the width of the heteropepaxial silicon strain resistor to its thickness. The use of strain gages with the ratio of their width b to thickness h, determined depending on the hole concentration by the formula

Description

1H

The invention relates to a measuring technique and can be used to convert mechanical quantities into an electrical signal, and is an improvement of the known strain gauge according to the author No. 934257

The purpose of the invention is to increase the points. measurements in a wide range of d temperatures due to a decrease in the spread of the values of the temperature error of sensitivity} due to the technological spread of hole concentrations in strain gages. 15 The essence of the additional image is that the reduction of the spread of the values of the specified value is achieved by using its dependence on the ratio of the width of the ten-resistor b to its thickness h

FIGURE shows a strain gauge,

cross section; fig 2 - depending

temperature coefficient

resistance (TKS) and temperature 25

of the coefficient of stress sensitivity (TKT) on the value --- for strain gauges made of silicon with a hole concentration of 7.0 x 30 x 10 cm; Fig. 3 shows experimentally obtained values of values of b / h and P / PQ) at which the sensitivity of a strain gauge with a bridge strain gauge fed from the gene ™, a current rator, does not depend on temperature; in fig. 4 - strain gauge; Fig. 5 shows temperature dependences of sensitivity of converters.

The modern technology of doping epitaxial silicon films on sapphire substrates allows to obtain a specified value of hole concentration with an error in the range of 45 i: 13%, which gives a variation in the temperature error of the sensitivity of the strain gauges around a zero value in the range of 10.05% However, mechanical and thermal deformations of the substrate in the direction perpendicular to the axis of the strain gauge (fig1) are not completely transmitted to its volume. The smaller the value of b / h, the smaller it is for a given deformation of the substrate. its value the transverse strain gage, so these elektrofizi ™ cal harakterist1-1ki geteroepitak50

,

d 5 0

five

Oh oh

five -

0

sial strain gages, such as TKS and TKT, depends on the magnitude b / b. This allows, by affecting the value of b / h, to reduce the variation of the temperature error of sensitivity of the strain gages during their mass production (Fig. 2 and H). The relationship of the values of b / h and P / Pd (Fig 3) is described by the empirical formula b / li (P / PO) .5 where is the hole concentration providing the zero temperature coefficient of sensitivity of strain gage transducers (b / h 7 / 40) by resistance strain gages and depending on the material of the elastic elemento. As can be seen from fig. 3, for any hole concentration from the interval (o, 7 l, 0) pjj, one can indicate such a value — the magnitude b / h from the interval (W - 40); which sensitivity of strain gauge does not depend on temperature

The proposed semiconductor strain gauge (Fig „4) contains an elastic element 1, made in the form of a circular sapphire membrane fixed on the contour, on the surface of which heteroepitaxial silicon teresistors 2 are located - conductivities connected in a bridge circuit. ,

The sapphire membrane plane has a crystallographic orientation (1012), the strain gauges are located in the (001) plane of silicon and are oriented along the crystallographic directions of 1107 silicon, the sensitivity of such strain transform, at PJ 7, and b / h -7 40 practically does not depend on temperatures in the range from -50 to 250 ° C (, curve a) o Taking into account the technological variation, the layers of silicon on different sapphire substrates have a hole concentration from 5 10 to 7 ,. x X 10 cm-,

Strain gages are made from a 2-3 μm thick layer of silicon by known photolithography methods. To ensure the required value of b / h, specific values of silicon thickness, h and PO-P hole concentration are chosen before photo photolithography. template providing during

3141

photolithography of the required value of b / h. FIG. 5 shows the temperature dependences of the sensitivity of converters, the strain gauges of which are made of silicon with a single hole concentration p 0.88 5.7 X

ten

cm

-3

but have

values

5 (curve b) n b / h 40 (. Ii wa c) o

Thus, by choosing the required value of b / h, one can decrease the temperature error of sensitivity of strain gauges by several times.

Claims (1)

Invention Formula Semiconductor strain gauge auth.St. No. 934257, about the t that is th increase measurement accuracy in a wide range of temperatures by reducing the scatter of temperature values sensitivity errors due to technological variation of hole concentrations in strain gages, the latter have a ratio of width width to thickness h, determined by B depending on the concentration of holes from the expression (I.-2 -) - at 0,7.-E- 0,975j of PORO 540 with 0.975 2-; one, RO - critical concentration of holes, providing a zero temperature coefficient of sensitivity of strain gauges with wide (b / h 40) strain gages. B h where r. A / U /, / /, / / /, u, / / l X. /, / /) - A ,, u have. // I ./X / ,,. / ,, JL TKS, GKT,% / Y 0.2 -0,2 ABOUT 20  ,, y / / ./X / ,,. / ,, JL 0 60 80 B / h a% .2 W 0.7. 0.80.3 / U8. J V p / p Fy fO 50100150 ig.5 200 t.C