Reproducibility of germanium resistance thermometers at 4.2 °K

Abstract

NBS has needed a set of very reproducible ge rmanium res is tors t.h a t would be c apab le of maintaining temperat ure scales. This paper desc ribes our p roce dure for se lec tin g s uc h a se t.A group of germani um resistors from thre e co mm er cial so urces hav e bee n the rmally c yc le d betwee n 4.2 oK and room temperature. The res istance-te mp e rature calib ration s a t 4.2 oK we re mad e with reference to a liquid helium bath so that reproducib le te mp e ratures c ou ld be d e te rmin ed froill liquid he lium vapor press ure meas ure me nt s. Seven res is tors out of 25 de mon s trat ed rep rodu c ibiliti es (o f th e 4.2 oK calibration) of about 0.001 oK aft e r und e rgoing th e multipl e c yc ljn gs. Guid e d by th ese res ults, we procu red tw e lv e, ne w, s imilar res istors whi c h were cyc led in a co mpa rab le procedure .After 85 cyc les, in whi c h 14 resis tance-te mp erature c ali brations we re pe rform e d at 4.2 oK for e ac h res is tor, 10 of th e 12 res is tors de mon strat e d rep rodu c ibiliti es of ap lJrox im a te ly 0.001 oK.Th e res ulting set of seco nd a ry th erm ometers have und ergo ne calibrati ons in th e te mp e rature ra nges, 2 105 OK a nd 2 to 20 OK ; re port s of thi s work will b e publi s he d in th e nea r future.Key Word s: Ge rm a nium res istors, ge rmanium res is tor rep rodu c ibility , low temperature th ermometry, re produ c ibilit y of ge rm a nium res is tors, th e rmal cycling at low temperature , I he rmom e t ry.

Germanium resistance thermometry in the range 2.1 to 5.0 K

“…However it does serve as an inte rpolati on aid th at can be cautiously used until a more meaningful representation is achieved. In the immediate fut ure we s hall see k to find im proved function s not only for the data presented in thi s paper but for more ex te nsi ve calibrati on data (2.3 to 20 O K) that we have previously publi s hed [1] _…”

“…sis tors in a highly stabilized liquid helium bath, has been described in an earlier paper [1]. While tbe 1M.…”

“…That is, th e resis tors have bee n th erm ally cycled from room te mperature to 4_2 O K and syste mati c calibrations of resistan ce and te mperature perform ed at 4.2 oK. Th e me thod s of cycling and calibration have bee n previously describe d [1], and th e re producibiliti es of parti c ular resistors were s tated. Th e previou resistor id e ntific atio n symbols will apply to precisely the same resis tors in this report.…”

“…Re sistors 1, 2, and 3 (reproducible to a pproximately 1 mdeg under ther mal cyclin g [1]) have bee n calibrate d simultaneously in the "constant te mperature" helium bath from 2.1 to 5.0 O K at inte rvals of 0.1 O K; th e res ults are liste d in table 2_ A log-log plot of r esis tan ce vers us temperature for #1 , # 2, and #3 , shown in fi gure 3, s uggests the possibility of re prese nting th e calibration data by a polynomial of th e form press ure th aI were obtain ed with a jacketed vapor press ure th er mome ter. Consequently, the resistance temperature calibration data (obtained from the bath calibration) were programmed on a computer for a least squares fitting to the above polynomial.…”

“…We have a group of impurity-doped germanium resistors that possess desirable thermometric properties at low temperatures -negative coefficient of temperature, good sensitivity and excellent reproducibility under thermal cycling [1).2 This paper describes the calibration (in the range 2.1 to 5.0 O K) of the abovementioned resistor group.…”