EXHIBIT 10.91

                                PROMISSORY NOTE

US$10,000,000.00                                  May 6, 1997
                                                  San Francisco, California

          FOR VALUE RECEIVED, Southwall Technologies Inc. (the "Company") hereby
unconditionally promises to pay at the times set forth in the Agreement referred
to below and in any event on Final Maturity Date to the order of The Sanwa Bank,
Limited,  San Francisco  Branch (the "Bank") the principal amount of Ten Million
United States Dollars  (US$10,000,000.00).  The Company promises to pay interest
on the unpaid  principal  amount of the Loan at such interest  rates and on such
dates as are provided for in the Agreement.

          All  such  principal  and  interest  (including  interest  on  overdue
principal and, to the extend  permitted by law, overdue interest and any and all
other amounts  payable by the Company under the terms of the Agreement and which
are not paid when due) shall be payable in lawful money of the United  States of
America  at the times and  places,  and in  accordance  with the  payment  terms
contained in the Agreement. Principal may be prepaid only in accordance with the
terms and conditions set forth in the Agreement.

          Each  payment  made on account of the  principal  of the Loan shall be
recorded by the Bank on its books and, prior to any transfer of this  Promissory
Note (the "Note"), endorsed by the Bank on the schedule attached to this Note or
any  continuation  of such  schedule  (provided  that the failure by the Bank to
make, or any error in making,  any such endorsement shall not limit or otherwise
affect the obligations of the Company under this Note with respect to the Loan).

          This Note is the  Promissory  Note referred to, and is entitled to the
benefits of, that certain Credit Agreement dated as of May 6, 1997 (as it may be
amended from time to time)  between the Company and the Bank (the  "Agreement").
Terms defined in the Agreement  are used in this Note with  respective  meanings
assigned to those terms in the Agreement.

          This Note shall be  construed in  accordance  with and governed by the
laws of the State of California  applicable  to contracts  made and performed in
the State of California.

                                              Southwall Technologies Inc.

                                              By: /s/ Martin Schwartz
                                                 -------------------------------
                                              Name: Martin Schwartz
                                              Title: President



<PAGE>

Letter of Guarantee
Submitted to The Sanwa Bank (Headquarters)

Attn: The Sanwa Bank, Limited

                              Letter of Guarantee

With regard to the  following  loan  extended by your San  Francisco  Office and
borrowed by Southwall Technologies, Inc., we, Teijin Limited, hereby jointly and
separately guarantee the performance of the borrower's  obligations and will not
cause The Sanwa Bank, Limited any damage or loss.

When The Sanwa Bank,  Limited  requests Teijin any payment relating to the loan,
Teijin will promptly pay and perform based upon its obligation under this Letter
of Guarantee.

1. Amount of Loan:
     US $10,000,000.00

2. Starting Date of Loan:
     May 6, 1997

3. Ending Date of Loan:
     November 6, 2004

                                             April 30, 1997

                                             Minamihonmachi-1 Chome 6-7 
                                             Chuou-Ku, Osaka

                                             Teijin Limited

                                             Hiroshi Itagaki
                                             President & CEO